Acne Miliaris Necrotica

Acne Necrotica Miliaris is a superficial, non-scarring inflammatory disorder of the hair follicles. It is one of two syndromes that falls under the broader clinical term Acne Miliaris Necrotica (AN), the other being the deeper, scarring Acne Necrotica Varioliformis. Since first being described in 1851, AN has proven to be a rare condition, prevalent among adult males, with chronic symptoms that wax and wane over time.

Both Acne Necrotica Miliaris and Acne Necrotica Varioliformis are characterized by pruritic follicular papule that are often triggered by stress.¹ Patients tend to be men aged 30 to 50, although the lesions have been reported in women and patients younger than 30 who have passed puberty.

Acne Necrotica Miliaris is characterized by minute, intensely itchy pustules on the scalp that may become sore and crusted due to constant scratching.² The lesions may concentrate around the frontal hairline (acne frontalis), but can appear anywhere on the scalp. They also vary in number from just a few to numerous pustules covering the scalp. Additional lesions may be found on the face, neck, chest, or back.³

Acne Necrotica Miliaris affects only the superficial portion of the hair follicle, allowing for hair regrowth following successful treatment, which can include oral antibiotics, topical corticosteroids, and oral isotretinoin, which has shown a rapid reduction of the pruritic lesions.⁴

Acne Necrotica Varioliformis is characterized by erythematous follicular papules that undergo necrosis (or cell death). These deeper lesions may progress to crusting, dry, dark scabs that leave smallpox-like scars (varioliformis) in their wake. Permanent hair loss may occur where the scalp has

been scarred (cicatricial alopecia).

Histological studies of an early lesion show lymphocytes (white blood cells) and plasma cells centered around a central hair follicle. The lymphocytes then fuse into the external root sheath. The keratinocytes within the external root sheath and surrounding epidermis show extensive cell necrosis.⁵

The true etiology, or cause, of AN is unknown, however, it has been postulated that the initial lesions are inflamed hair follicles with Propionibacterium acnes. (Propionibacterium acnes are slow growing anaerobic bacterium which are linked to the skin condition acne.⁶ They are gram positive, which means they stain dark blue or violet with gram staining. Gram positive bacteria generally have a single lipid bilayer called monoderms.)

The lesions may also be caused by an abnormal reaction to the Staphylococcal Aureus Bacteria and the Streptococcal Bacteria, which live on the skin at all times but can cause infection when they enter the body through a cut or other injury. Gram-negative bacteria, which usually originates in the nose following antibiotic treatment for acne, may also be to blame, as is Tinea Capitis (ringworm of the scalp), caused by a fungus that invades the hair shaft. In at least one case, use of the drug phenylbutazone was believed to have caused the syndrome.⁷ In still others, extreme mechanical manipulation of the scalp due to scratching or rubbing patches of underlying folliculitis may be to blame, as are the tiny parasitic mites, demodex folliculorum. However, the most common pathogens found in pustules remain Staphylococcus aureus and Propionibacterium acnes.⁸

Examining the scalp and forehead for past umbilicated scars with a “punched-out” appearance is helpful to the trichologist working toward a diagnosis of AN. In addition, the presence of Staphylococcus aureus and Propionibacterium acnes should be determined in erupting pustules. In the case of Propionibacterium acnes, Isotretinoin should be tried, while in the case of Staphylococcus aureus, anti staph agents and oral tetracyclines may prove successful.⁹

Sources

Dawber, Rodney, Ed., Diseases of the Hair and Scalp, Third Edition, Blackwell Science, Malden, MA, 1997.

DermNetNZ.org

HairScientists.org

Olsen, Elisa A.,Ed., Disorders of Hair Growth, Second Edition, McGraw-Hill, New York, 2003.

Wikipedia.org

1 Dawber, Rodney, Diseases of the Hair and Scalp, p. 511.

2 DermnetNZ, Scalp Folliculitis, http://dermnetnz.org/acne/scalp-folliculitis.html

3 Olsen, Elisa A., Disorders of Hair Growth, p. 111.

4 Olsen, Elisa A., Disorders of Hair Growth, p. 383.

5 Olsen, Elise A., Disorders of Hair Growth, p. 112.

6 Wikipedia.org, Propionbacterium Acnes, http://en.wikipedia.org/wiki/Propionibacterium_acnes

7 Zemite, Inga, http://www.hairscientists.org/acne-miliaris.htm

8 Zemite, Inga, http://www.hairscientists.org/acne-miliaris.htm

9 Zemite, Inga, http://www.hairscientists.org/acne-miliaris.htm

What To Expect When Visiting A Trichologist

If you were to visit a trichologist complaining of thinning hair, you could expect the following type of examination:

First, the trichologist would gather some personal information including your health history. She would pay particular attention to any health issues you had experienced within the last two to three months including: illnesses, beginning or ending medications, childbirth, breastfeeding, diet, stress, and regular menstrual cycles. She would also ask about your family’s health history and whether your relatives experienced any significant hair loss.

Next, the trichologist would ask how you care for her hair: what types of products you use and how often, whether you chemically process your hair, swim regularly, or wear your hair in any tight hairstyles.

The trichologist would then physically examine your hair and scalp to look for any signs of patchy hair loss, scaling, swelling or redness. Once she had ruled out those symptoms, she would begin to examine you for a condition called diffuse hair loss – thinning caused by hair loss from all over your head.

 The trichologist would run her hands over your hair to check for signs of thinning. She would then gently pull on your hair in several different areas to see if it indeed came out easily and in quantity. At the same time, she would ask when you last washed or brushed your hair and explain that it’s perfectly normal to lose up to 150 hairs a day, many of them while shampooing or grooming.

The trichologist would save the hairs she gathered in an envelope marked with the your name while explaining that she would examine them under a microscope after the appointment. She would then take several digital photos of your hair to upload to her computer.

At the end of the initial appointment, the trichologist would explain that she suspected diffuse hair loss (telogen effluvium). She would set you at ease by explaining that you would not go bald with the problem and that she may be able to correct the cause and restore your hair’s thickness. She would schedule a follow-up appointment at which time she would report her findings.

When examining the hairs under a microscope, the trichologist would look to see if there were white bulbs at the ends, indicating telogen hairs (hairs in the “fall out” phase). She would also check for small anagen bulbs (hair in the active growth phase) without root sheaths, which would indicate a condition called loose anagen syndrome. Lastly, she would look for signs of breakage, which could indicate anagen effluvium, or chemical or mechanical damage to the hair.

If the trichologist determined that you were suffering from breakage and appeared to have no outstanding health or nutritional problems, she would recommend gentle care of your hair at home and in the salon, as well as protecting it from UVA/UVB rays.

Breakage due to signs of fungal infection or inherited defects would require further investigation and a gentle explanation that there is no treatment.

If the hairs appeared to have fallen out in the active growth stage (anagen) and you had undergone cancer treatment (radiation and chemotherapy), or may have been exposed to toxins, the trichologist would tell you that the hair loss should stop two to three months after either the treatments stopped or your doctor treated you for toxicity.

If the trichologist suspected any of the following, she would refer you to your physician for a blood test and a complete medical check-up:

• Hormonal imbalance
• Thyroid problem
• Diabetes
• Anemia
• Lupus
• Poisoning from X-rays, pesticides, lead, or mercury
• Thrush
• Kidney or liver problems.

For more information on Trichology, visit The Trichological Society's website.

Changing Hair From The Inside Out

If you always wished you had straight or curly hair, you may soon be able to have your wish simply by popping a pill. Scientists at L'Oreal say it's possible to alter the hair bulb deep in the follicle and actually change the shape of your hair from naturally curly to straight, and vice versa. They're working on a hormone pill that would transform “hook-shaped” bulbs responsible for curly hair into straight-shaped bulbs that produce straight hair. They also say this same technology can be used to turn gray hair back to its natural color.

Hair Properties and Ethnicity

Natural hair types, colors, and textures are the result of the genes passed down from our ancestors. Scientists have identified three main races that influence hair types today: Mongoloid, Caucasoid, and Afroid.

• Mongoloid: Mongoloid hair originated with people from the Orient. It is very straight, coarse, and black in color. Perfectly straight keratin bundles and a round hair shaft account for the thick, straight texture. 
• Caucasoid: Caucasoid hair is more varied in appearance, since Caucasian ancestors range from fair-skinned people of northern Europe all the way down to India. Caucasoid hair ranges from the palest blonde to the darkest black, as well as wavy, straight, curly, thick, or thin. An oval hair shaft with straight or wavy keratin bundles may account for the variety of Caucasoid hair.
• Afroid: African hair comes in varying degrees of black and brown coils. The hair shaft may be oval and the cuticle sharply kinked at the edges. African hair can be dry and easily damaged due to its twisted structure and inability for sebum to easily lubricate the hair shaft.

All hair twists as it grows, and scientists believe it is the number of twists that determines how curly it will be. Scientists have found that some Afroid hair has 12 times as many twists per centimetre as some Caucasoid hair.¹

Hair gets its shape depending on the shape of the hair follicle and the opening to the scalp or skin. The final shape of the hair follicle occurs as the keratin hardens and both disulphide and hydrogen bonds hold it in place.

Disulphide Bonds: As discussed earlier, disulphide bonds are extremely strong and give hair their permanent shape. These bonds can only be broken and hair texture changed with strong chemicals like perms and relaxers.

Hydrogen Bonds: Hydrogen bonds also exist within keratin and are much weaker than disulphide bonds. They give hair flexibility and can be easily broken with water. The hydrogen bonds reform themselves as they dry, allowing for temporary hair styling with rollers and other methods.

Whether hair appears dense or sparse on the head usually depends on two factors: how many hairs a person has and how thick the diameter of the hair shaft is. The number of terminal hair-shafts on a head ranges from 100,000 to 150,000. Natural redheads tend to have the least amount of hair while blondes have the most.

Interestingly, National Geographic reports that in our world of 7 billion people, the most “typical” person is a 28-year old Han Chinese male.¹ That means that the most typical hair type in the world today is straight, black, and Asian. By 2030, however, the most typical human – and hair type – will be Indian.

Natgeo.com, Have You Seen Him? http://www.thelifefiles.com/2011/03/05/have-you-seen-him/

P&G Beauty & Grooming, Hair Types, http://www.pgbeautygroomingscience.com/hair-types.html

The Hair Growth Cycle

Each hair has a life cycle in three distinct phases: anagen, catagen, and telogen. These phases occur concurrently in individual hairs, preventing hair from all falling out at once.

• Anagen (growing): Anagen is the active growth phase, which can last 1,000 days or more without interruption. On average, hair grows an average of ½ inch per month, or 6 inches in a year. As humans age, the anagen phase may shorten, producing shorter, finer hairs that may result in the appearance of thinning. How long a person’s hair grows depends on genetics and varies between genders. The Anagen phase occurs in several stages. Stages 1 through 5 are known as proanagen, and stage 6 is known as metanagen.
• In stage 1, cells at the bottom of the epithelial sac (the “secondary germ”) begin mitotic activity (cell division).
  In stage 2, the lower part of the follicle grows down and encloses part of the dermal papilla. Cells in the dermal papilla enlarge and become separated by an extracellular matrix. At the same time, the inner root sheath appears as a keratinized structure overlying the matrix.
  In stage 3, the keratinizing inner root sheath takes on a conical shape and the cortex starts to differentiate. Tyrosinase activity and melanogenesis begin the process of melanin production in melanocytes located in the matrix.
  In stage 4, cortical cells begin to become pigmented, while the cortex continues to keratinize.
  In stage 5, the hair shaft penetrates the inner root sheath at the sebaceous duct.
  In stage 6, the follicle is fully developed.
  Healthy hair growth is also contingent on proper nutrition and overall good health. Hormones also play an important role in determining the length of the growth cycle with thyroid  hormone speeding up growth in resting hair follicles and androgens (male hormones) affecting hair growth and thickness. Oestrogen slows hair growth but makes the anagen phase last longer, which is why many pregnant women report longer, lusher hair.
  • Catagen (intermediate): Melanization stops just prior to the catagen phase, which occurs when mitosis in the matrix decreases and then stops. This short phase lasts for approximately 10 days. During this time, keratinization of the hair shaft continues and the terminal portion of the hair becomes club shaped. This club remains unpigmented.¹ The base of the follicle and the club hair continue to move upward while the inner root sheath disintegrates. The vitreous (or “glassy”) membrane that is the basement membrane of the outer root sheath, thickens during this phase, while the dermal papilla loses its blood supply and extracellular matrix.
  • Telogen (resting): Telogen lasts for some 100 days during which the club is held in the epithelial sac. The dermal papilla, now devoid of its blood supply, appears as a tightly packed ball of cells. As a new hair grows it may push out the old hair, causing it to fall painlessly. At any given time, up to one in ten hairs on a human head is in the telogen phase.² It’s perfectly normal to lose up to 150 hairs each day through shedding without worrying about hair fall being excessive.
  1 Dawber, Rodney, Diseases of the Hair and Scalp, p. 7.
  2 P&G Beauty & Grooming, The Hair Growth Cycle, http://www.pgbeautygroomingscience.com/the-hair-growth-cycle.html

Hair Embryology

In humans, hair follicles first begin to develop in the eyebrows, chin and lip areas when a fetus is between 9 and 12 weeks gestation.¹ In the “pre-germ” stage of development, epithelial cells crowd in the basal layer of the epidermis. Mesenchymal cells (undifferentiated stem cells that differentiate into a variety of cell types) cluster beneath the epithelial cells, which then elongate to form the hair germ. As the hair germ enlarges, it grows downward and becomes asymmetrical. The solid column of cells is known as the hair peg.

          The hair peg contains a broad, concave tip with mesenchymal cells that eventually form the dermal papilla and dermal sheath. The lower end of the hair peg eventually becomes bulbous, and the tip’s cavity deepens further to enclose the dermal papilla. The bulbous hair germ will go on to form the hair bulb matrix, while the mesenchymal cells surrounding the bulb will form the 

dermal sheath. The entire development of the hair follicle is completed by about 22 weeks of gestation.

Two enlarged areas then appear at the bottom of the follicle: the top enlargement is the precursor of the sebaceous gland and the lower bulge is the future site of the arrector muscle attachment. In some follicles (in the areas including the groin, areolae and face), a third bulge appears above the sebaceous gland enlargement to form gland.

Above the hair bulb matrix, a cone of cells differentiates from the matrix and goes on to form the cortex and cuticle of the hair.

1 Dawber, Rodney, Diseases of the Hair and Scalp, p. 3.

Types of Hair on the Human Body

There are three types of hair in humans: lanugo, terminal and vellus.

• Lanugo Hair: Lanugo hair (foetal hair) develops at about the third month post conception. These hairs grow at the same rate all over the baby’s body are very fine, and lack a medulla. They shed in favour of vellus hair at 36 to 40 weeks of gestation.
• Vellus Hair: Vellus hair is short, fine hair that may be hard to see with the naked eye. These hairs develop in the womb about 4 weeks before a baby is born. They appear on most every part of the body except for the lips, back of ears, palms, soles, the naval, scar tissue, and some parts of the external genitalia (are they on eyelids?). The hairs are usually no longer than 2 mm long, do not have a medulla, contain little or no pigment, and are not attached to a sebaceous gland (glands in the dermis that secrete an oily/waxy substance called sebum to lubricate the hair and skin). Vellus hair acts as thermal insulation for the body.

• Terminal Hair: Terminal hairs are found on the head and other parts of the body and grow from follicles with sebaceous glands. During puberty, an increase in androgen hormones causes many vellus hairs to be replaced by longer, darker terminal hairs in both men and women, although men usually develop them in more places. These include the face, pubic area, armpits, abdomens, legs and arms. Terminal hairs often contain a medulla.

Terminal hairs are affected by both sweat and sebaceous glands.

A. Sweat Glands: Two types of sweat glands exist in humans, eccrine and apocrine glands.

1. The eccrine glands cool the body by producing sweat, a watery liquid comprised of the chemicals or odorants 2-methylphenol (o-cresol) and 4-methylphenol (p-cresol), as well as a small amount of urea, that exits the pores on the epidermis and evaporates. These glands also supply the skin with a constant supply of water and nutrients. It is believed that humans have between 2 and 5 million sweat glands in the body, with the highest concentration in the palms of hands, soles of feet, forehead, and underarms. The scalp and forehead also sweat through the eccrine glands. Eccrine glands do not require a hair to exit the body, instead relying on individual pores.

2. The apocrine glands are the larger of the sweat glands. They may extend as deep as the hypodermis and produce an odor that allows mammals to recognize one another. They may also serve sexual stimuli function. These glands are considered “primitive” and become fully functional at puberty. Apocrine glands are found in the arm pits, the areola, and the anal region, with their ducts opening into the canals of the hair follicles. The sweat is secreted into the upper parts of the hair follicle and exits to the skin via the hair shaft.¹

B. Sebaceous Glands: In humans, sebaceous glands exist in conjunction with hair and are most prevalent on the scalp and face (approximately 400 to 900 per square centimeter). They secrete an oily substance called sebum which lubricates, waterproofs and protects the hair and skin. Androgens (male hormones) are important factors in determining the amount of sebum secreted from sebaceous glands all over the body.

The word Sebum is Latin for “fat” or “tallow.” It is, indeed, made up of fat in the form of lipids, as well as wax and dead cells. Specifically, sebum is 25% wax monoesters (usually derived from an acid), 41% triglycerides, 16% free fatty acids, and 12% squalene (a biochemical precursor to a family of steroids).

Sebum itself is odourless, but odour can occur once it’s broken down by bacteria. In the sebaceous glands, sebum is produced in cells that eventually burst and release the sebum through a small duct leading from the gland to the hair shaft. This bursting action classifies sebaceous glands as holocrine glands (along with the meibomian glands of the eyelids)

A build-up of sebum can give the hair and scalp a greasy appearance and is usually the result of poor hygiene or the onset of puberty. In this case, higher level of male hormones (androgens) can cause sebum production to kick into overdrive.

1 Dermaxine.com, Sweat Glands, http://www.dermaxime.com/skin-sweat-glands.htm

Chemical Composition of Hair

Hair is made up mostly of protein, which accounts for some 65 to 95% of its weight. These proteins contain the following amino acids in normal hair:

Amino Acid Amount

Lysine 2.8

Histidine 0.8

Arginine 5.6

Aspartic Acid 5.0

Threonine 6.9

Serine 11.7

Glutamic Acid 11.1

Proline 3.6

Glycine 6.5

Alanine 4.8

Cystine 17.5

Valine 5.9

Methionine 0.5

Isoleucine 2.7

Leucine 6.1

Tyrosine 1.9

Phenylalanine 1.4

It is also made up of the following elements: Ca, Mg, Sr, B, Al, Si, Na, K, Zn, Cu, Mn, Fe, Ag, Au, Hg, As, Pb, Sb, Ti, W, Mo, I, P, Se.

Lipids: sebum, free fatty acids, and neutral fats esters, glycerol, waxes, hydrocarbons, and alcohols.

Water: Hair has the capacity to absorb water, increasing its weight between 12 - 18%.

Hair Structure

Hair has two distinct parts: the hair follicle and the hair shaft.

Hair Follicle: The hair follicle is a tiny pit located in the fat of the scalp from which the hair grows and is recognized as a separate entity within the skin.¹ The hair follicle is divided into two regions, the Hair Bulb and the Mid-Follicle Region.

The Hair Bulb: The hair bulb is situated inside the follicle and contains the hair matrix with actively dividing and growing cells that are rich in RNA, as well as the dermal papilla. The matrix is a group of epithelial cells combined with pigment-producing melanocytes. Cells in the matrix are some of the fastest growing cells in the human body.²The cells are several layers deep with an active turnover rate – researchers believe that each matrix cell divides every 23 to 72 hours.³ Active cell division takes place in the lower bulb and the upper bulb that is adjacent to the dermal papilla.

The dermal papilla is the vascularized, growing part of the hair made up of the connective tissue sheath and the vitreous membrane. The lower part of the dermal papilla connects to the fibrous root sheath. The cells surrounding the dermal papilla are precursors of the hair fiber.⁴ The size of the papilla is directly related to the size of the hair that is produced. In terminal follicles in the anagen phase, the dermal papilla is attached to a basal plate of connective tissue via a stalk containing papillary blood vessels. Researchers believe that the dermal papilla may determine the cyclical growth of each hair follicle.⁵ The papilla is considered the “communication link” between the hair follicle and the rest of the body.⁶ Capillaries allow blood and nutrients to pass through the papilla. If the papilla is destroyed, no further hairs will grow from that follicle.

As the cells grow out of the matrix, they push previously formed cells up toward the surface of the hair and scalp in a process of layering, hardening, and keratinizing. As the cells reach the upper part of the bulb, then arrange in layers: the outer three layers become the inner root sheath that lines the inside of the follicle, while the remaining three layers of cells become the hair’s cortex, medulla, and cuticle.

• Inner Root Sheath: The inner root sheath consists of the Henle layer (a single layer of cubical cells with clear flattened nuclei)⁸, Huxley layer (up to two layers of horny, flattened, nucleated cells)⁹, and the internal cuticle, which is one cell thick. The cuticle of the inner root sheath is interlocked with the hair cuticle via overlapping shingles, or cuticle cells, firmly anchoring the growing hair in the follicle. All three layers are formed from the matrix cells in the hair bulb. All three layers undergo differentiation at the same time, but at different rates with the Henle layer first, followed by the Huxley layer, then the cuticle. Thus, complete hardening and differentiation of the inner root sheath occurs before the layers of developing hair.¹⁰
• Outer Root Sheath: The outer root sheath surrounds the inner root sheath where the sebaceous duct enters the hair follicle. All of the cell layers within the outer root sheath are produced by the hair matrix.¹¹ However, the outer root sheath itself is not a product of the hair matrix. It consists of a sleeve of cells structured like the surface epidermis. The Outer Root Sheath is divided into two parts: a short lower part surrounding the outer part of the bulb (approximately one or two cells thick), and the upper part that reaches from the neck of the bulb to the sebaceous duct.¹² Although the exact function of the outer root sheath isn’t fully known, the outward migration of its cells may help facilitate the final movement of the terminal part of the hair at the end of the catagen phase.

Most terminal hair follicles are attached to arrector pili muscles, which are controlled by sympathetic nerves. They contract involuntarily under stress and allow the hair to “stand on end” as goosebumps. The arrector pili muscle is attached to the follicle below the sebaceous duct.

• Connective Tissue Sheath: The connective tissue sheath is a continuous thin layer of tissue that surrounds the base of the hair follicle, the sebaceous glands, and the papillary layer of the dermis.¹³
• The Vitreous Membrane: The vitreous or “glassy” membrane is the basement membrane of the outer root sheath that separates the outer root sheath from the connective tissue sheath. The vitreous membrane thickens during the catagen phase of hair growth.
• The Fibrous Root Sheath: Surrounding the vitreous layer is the fibrous root sheath consisting of bundles of thickened collagen. This is the outermost layer of the hair follicle that covers the hair follicle from the dermal papilla at the bottom to the papillary dermis above.
• The Mid-Follicle Region: Above the hair bulb is the mid-follicle region. This is where the growing cells die and harden and are pushed out of the skin by the growing cells below.

Hair Shaft

The hair shaft can be seen above the skin or scalp and consists mainly of dead cells, binding material, and water. It is made up of three layers: the cortex, medulla, and cuticle.

• Cortex: The cortex makes up the main bulk of the hair. It is at the very center of the hair shaft made up of long, vertical strands of low-sulfur keratin and are compressed into larger bundles called macrofibrils that are held together by sulphur-rich keratin.¹⁴ This combination lends the hair its super strength (a single hair can support around 100 grams – 3.5 ounces – without breaking). The cortex also contains pigment granules called melanin that is formed in special pigment-producing cells called melanocytes during the growth phase. There are two forms of melanin: eumelanin and phaeomelanin.

Eumelanin: Eumelanin exists as oval-shaped granules that give black and brown hair their dark pigment. These granules are hard in consistency and have sharply defined edges. The more Eumelanin that is present, the darker the hair will appear.

Phaeomelanin: This is a light pigment found in blondes and redheads. Phaeomelanin exists as smaller, partly oval/partly rod-shaped granules.

Differences in hair color depend on which type of melanin and how much is present in the cortex. Gray hair contains only a few melanin granules spread throughout the cortex while perfectly white hair has none. The graying process occurs when melanin production in the hair bulb gradually tapers off. Premature graying (in the 20s or 30s) usually happens as a result of a medical condition  or a particular gene.

• Medulla: Some, though not all hair shafts, contain a medulla, a hollow core that helps regulate body temperature. The actual structure includes a cortex-like framework of spongy keratin that supports thin shells of amorphous material. Scientists believe the medulla is a “throw back” to the time when our ancestors needed this extra insulation.¹⁶
• Cuticle: The cuticle is the outer protective layer of the hair-shaft that resembles tiles on a roof. It is made up of some 6 to 10 overlapping layers of long cells which circumvent the shaft, with their free margains pointing toward the hair tip. The cuticle contains three major layers: a cystine-rich A-layer, the exocuticle and the endocuticle. When the transparent cuticle cells lay flat, they reflect light and give hair its luster. Chemical and mechanical damage (sun exposure, brushing, heated tools) can cause the cuticle to lift, exposing the cortex beneath. This “weathering” weakens the hair shaft and can lead to splitting and breaking. A heavily damaged cuticle can become porous and cause hair to become excessively dry since the cortex can no longer retain the needed amount of moisture. Modern hair conditioners can smooth over the damaged cuticle to make hair appear healthier. In additional, panthenol (vitamin B5) can actually penetrate the scalp and hair shaft, providing much-needed moisture.

Covering the cuticle itself is a thin layer called the epicuticle. It is believed to be a lipid-containing surface membrane that may be chemically associated with the intercellular binding material.¹⁷

1 Dr. John Gray, The World Of Hair, p. 12

2 Wikipedia.org, Hair Follicle, http://en.wikipedia.org/wiki/Hair_follicle

3 Dawber, Rodney, Diseases of the Hair and Scalp, p. 23.

4 Dawber, Rodney, Diseases of the Hair and Scalp, p. 23.

5 Dawber, Rodney, Diseases of the Hair and Scalp, p. 32.

6 The International Association of Trichologists, The Hair and Scalp, p. 40.

7 The International Association of Trichologists, The Hair and Scalp, p. 40.

8 Wikipedia.org, Henle’s layer, http://en.wikipedia.org/wiki/Henle%27s_layer

9 Wikipedia.org, Huxley’s layer, http://en.wikipedia.org/wiki/Huxley%27s_layer

10 Dawber, Rodney, Diseases of the Hair and Scalp, p. 27-28.

11 Dawber, Rodney, Diseases of the Hair and Scalp, p. 23.

12 Dawber, Rodney, Diseases of the Hair and Scalp, p. 29.

13 The International Association of Trichologists, The Hair and Scalp, p. 45.

14 P&G Beauty & Grooming, Hair Structure, http://www.pgbeautygroomingscience.com/hair-structure.html

15 P&G Beauty & Grooming, Hair Color, http://www.pgbeautygroomingscience.com/hair-color1.html

16 P&G Beauty & Grooming, Hair Structure, http://www.pgbeautygroomingscience.com/hair-structure.html

17 Dawber, Rodney, Diseases of the Hair and Scalp, p. 35.

What Is Keratin?

The hair and nails are considered to be extensions of the skin and are both made of a hard, fibrous protein called keratin. As a part of the Integumentary System, the hair helps regulate body temperature, keeps the skin cool and moist, and responds to touch, while the nails protect the fingers and toes, and assist with grasping and holding.

Keratin is the building block of human skin, hair and nails, as well as hooves, claws, and horns in animals. It comes from the Greek keras, meaning horn. As with all proteins, Keratin has large molecules made up of smaller amino acids that join together to create the extremely hard protein.

Keratin is a family of fibrous structural protein (scleroproteins) with main duties to protect and support the body by forming connective tissue, tendons, bone, and muscle fiber.[1] The only other biological substance known to be as hard as keratin is the chitin that makes up the exoskeletons of anthropods.[2]

As a protein, keratin is made up of chains of amino acids, with high concentrations of the amino acid cystine. Each unit of cystine is made up of two cysteine amino acids in different chains which are linked together by two sulphur atoms. This chemical bond is called a disulphide linkage and many of them appear as rungs on the keratin ladder.[3] The disulphide bond is one of the strongest bonds that exists in the natural world.[4]

Keratin molecules assemble into bundles of intermediate filaments (a family of related proteins that share common structural and sequence features) which are extremely tough and insoluble. These filaments are the main component in keratinocytes (cells that have undergone keratinization) in the cornified layer of the epidermis.

Keratinization

Keratinization involves three kinds of epithelial (outer layer) cells: undifferentiated, differentiating, and terminal cells.[5] (Differentiation is the process by which cylindrical basal cells lose their nuclei, change their shape and composition, and become flattened, cornified cells).

• Undifferentiated cells are mitotically active. In the case of nails and stratum corneum, these undifferentiated cells continuously renew the keratinizing tissues. In the case of hair, they renew in cycles.
• Differentiating cells carry out four activities: synthesizing pre-keratin substances like tonofibrils (cytoplasmic protein structures), losing their nucleus and other elements in the cytoplasm, losing water, and uniting the cells into a horny mass.
• Terminal cells consist primarily of keratin and are completely inactive. They make up the final structures of hard keratin for the hair’s cuticle and cortex, and the soft keratins that make up the medulla and stratum corneum.

There are two types of keratin involved in keratinization: soft keratin and hard keratin.

• Soft Keratin (also known as beta type) is part of the stratum corneum of the epidermis (top layer of skin). It also creates the hair’s internal root sheath and medulla. Soft keratin is made of desquamating cells (desquamation: the process by which cells from the stratum corneum split apart, loosen, and fall away as they reach the top of the epidermis). Soft keratin has a high lipid (fat) content and lower sulphur content (less than 3%). Soft keratin contains more of the amino acid cysteine and less cystine than hard keratin, making it less stable in high temperatures.
• Hard Keratin (alpha type) makes up the hair and nails (as well as feathers and horns in animals). As its name suggests, it is tough and hard and doesn’t desquamate. Hard keratin has a lower fat content and higher sulphur content (more than 3%). It has good cell structure and is able to withstand heat.

In the nails, keratin is formed and hardened in the Matrix, the part of the nail bed beneath the nail root that contains nerves, lymph and blood vessels. Hard keratin formation for the hair

takes place in five stages and areas:[6]

1.      Germinal Matrix: Cells in the hair bulb’s germinal matrix are constantly dividing during anagen, or the active stage of hair growth. These cells move in rows to the upper part of the bulb where they become longer and larger and will eventually become the hair cortex.

2.      Differentiation Zone: The area of the upper hair bulb where the cells in the elongate and the nuclei shape changes from round to oval.

3.      Fibrilization Zone: Area above the upper bulb where the cells elongate.

4.      Keratinization Zone: Area of the hair shaft where the cells reach their maximum size. This zone has two distinct parts:

(a)   The lower zone: where the fibrous protein is complete but the structure is unstable (also called the keratogenous zone). Hydrogen bonding of amino acids takes place followed by disulphide bonds (the amino acid cysteine is oxidized to cystine), making the protein extremely strong.

(b)   The upper zone: Cells rapidly become stable and are able to withstand heat and chemicals.

5.      Keratinized Zone: By the time the cells reach this zone, they have lost approximately 80% of their water weight, which has been replaced by pockets of air.

[1] Wikipedia.com, Scleroprotein, http://en.wikipedia.org/wiki/Fibrous_protein

[2] How It Works Daily, http://www.howitworksdaily.com/science/question-of-the-day-what-are-our-fingernails-made-of/

[3] P&G Beauty & Grooming, Hair Strength, http://www.pgbeautygroomingscience.com/hair-strength.html

[4] &G Beauty & Grooming, Hair Strength, http://www.pgbeautygroomingscience.com/hair-strength.html

[5] The International Association of Trichologists, The Hair and Scalp, p. 57.

[6] International Association of Trichologists, The Hair and Scalp, p. 58-59.

Sources

About.com Dermatology, Skin Anatomy, http://dermatology.about.com/cs/skinanatomy/a/anatomy.htm

Buzzle.com, Integumetary System Functions, http://www.buzzle.com/articles/integumentary-system-functions.html

Dawber, Rodney, Ed., Diseases Of The Hair And Scalp (Third Edition), Blackwell Science Ltd., 1997.

International Association of Trichologists, The Hair and Scalp, I.A.T., Kalamazoo, 1993.

Natgeo.com, Have You Seen Him? http://www.thelifefiles.com/2011/03/05/have-you-seen-him/

Online Cosmetology School, Anatomy & Physiology of Skin, Hair, and Nails, http://www.cosmetologyschool.org/resources/anatomy-physiology-of-skin-hair-and-nails/

P&G Beauty and Grooming Science, The World of Hair, http://www.pgbeautygroomingscience.com/the-world-of-hair1.html

Sandia Corporation, Structure of the Skin, http://www.nmsl.chem.ccu.edu.tw/tea/SKIN_910721.htm.

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