Search Skin Biology
The Functions of Head and Facial Hair
Hair forms part of romantic and sexual attraction. Mermaids and sirens of the sea and the maiden Lorelei of the river Rhine are said to have brought men to disaster who became fixated on the beauty of their long tresses. Australian aborigines saved their wives hair clippings as a prized possession. Even today, some orthodox Jewish women only allow their husbands to see their hair.
What do we desire in hair? Humans generally are attracted to head hair that is relatively dense, thick-stranded, and somewhat long. Hair that is strongly pigmented (from blond to black) but not gray is generally preferred. The ideal of hair most closely approximates the physical characteristics of the hair on young child. Many conditioners add fats to thicken the hair shaft so it looks like younger hair.
Hair is a specialized form of skin as are nails, scales, feathers, horns, and claws. Hair grows over a large percentage of the human body surface serving protective, sensory, sexual attractiveness functions. Human beings have about 1,400,000 hairs on their body, with about 450,000 of them to be found above the neck. You have about 100,000 hairs on your head and normally shed 25 to 100 a day while growing the an equivalent number of new hairs. Another 30,000 reside in mustaches, beards, or whiskers.
Blondes have usually much more scalp hair than hair red or dark haired heads. A single hair has a thickness of 0.02-0.04mm, so that 20-50 hair fibers next to each other make one millimeter. Hair is as strong as a wire of iron. It rips after applying a force equivalent to 60 kg (130 pounds), after it stretched itself for about 70%.
Questions or Advice?
Email Dr. Loren Pickart at drlorenpickart@gmail.com
Call us at 1-800-405-1912 Monday Through Friday (8 am to 6 pm) PST
Hair Color: Blonde, Red, Brown, and Black
The hair roots or follicles contain pigment cells that, depending on your genetic background, creates a black pigment called melanin or eumelanin and a reddish pigment, produced by a separate gene, called heomelanin (or sometimes called phaeomelanin).
The greater the amount of pigment sent to the hair, the darker the hair becomes. if the amount of pigment is reduced, the hair color turns brown and then reddish or blond. Color changes with age. Most "towheaded children" who have blonde-whitish hair turn into brunet adults.
The shades of hair color are influenced by how light bounces off the hair proteins, but basically depends upon pigment contained within the hair shaft center or cortex.
Eumelanin is the pigment found in brown or black hair and to lesser degrees in blonde hair.
Heomelanin, produces red hair while and mix of eumelanin and heomelanin produces a blonde-red mixture or "strawberry blonde". When pigment is significantly diminished, the hair appears gray and when it is absent, the hair is white.
Under severe stress hair or malnutrition, hair can lose its color. In the trench warfare of World War I, there were cases of young men whose hair turned gray within two months after prolonged episodes of severe fighting and artillery bombardments.
Copper is the key nutrient in pigment (melanin) production in the skin and hair. A lack of sufficient dietary copper can cause hair to lose its color.
Hair Length and Growth
Hair grows at a faster rate in the spring and summer than in autumn and winter - a fact that often is used to "prove" that certain hair growth remedies stimulate hair growth. The growth rate is however very much related to the individual person, his age, diet etc. The lifetime of the anagen phase is responsible for the maximum of hair length you can have. Waist length hair takes about 5 years to grow out from a short hair cut, periodic trims included.
If your hair has a lifecyle of 2 years, you will never achieve a nice waist length mane. In rare families, long hair cycles are combined with rapid hair growth - producing floor length hair in women. At right is the person with the longest well documented record for hair length who is Diane Witt, a mother of two who lives in Worcester, MA. Her hair measured over 12 ft. 8 in. in March 1993.
| Hairs: | Average length (cm): | Growth rate per day (mm): |
| On the head | 70 | 0.35 |
| Eyebrows | 1.0 | 0.15 |
| Mustaches (beards or whiskers) | 28 | 0.4 |
| Armpit hairs | 5 | 0.3 |
| Pubic hairs | 4 | 0.2 |
The Structure of Hair
Mature hairs are biologic filaments composed primarily of proteins (88%) of a hard, tough, insoluble, fibrous type known as keratin. Proteins are built up from individual amino acids to form long chains where each amino acid is a link in the chain.
Two amino acids are joined together by a "peptide bond", and the correct number of amino acids placed in their correct order will form a specific protein; i.e. keratin, collagen, elastin, and so on.
The keratin found in human hair is also a major protein in fingernails. Three layers of keratin form every hair. The outer sheath of cuticle forms overlapping scales.
Hair proteins have a high sulfur content from the amino acid cysteine which can easily form cross-links to other cystines in the hair molecule. These bonds are responsible for the hair's toughness and abrasion resistance and the cross-links hold the hair fibers together.
As long as this organization is not disrupted, the fiber is strong and appears "healthy". The breaking and re-linking of cysteines in the hair protein is used to "perm" the hair to change its shape and add curl to the hair.
Chemicals applied to hair and mechanical flexing of hair can sometimes damage the structure of these biologic filaments and cause the hair to have an undesirable appearance, be less manageable, or be more vulnerable to breakage.
Care of Hair Fibers
Chemical and mechanical injuries to the hair or scalp can produce a number of different effects. Tight hairstyles, hot combs, hot oil treatments, and harsh use of hair blowers can all produce damage to the hair fiber.
One should be aware of potential consequences when manipulating hair and to exercise caution.
The typical chemicals used to alter hair include bleaches, dyes, relaxers, and agents used for permanents. Any of these chemicals can cause some degree of hair damage but, with care, most cosmetic products produce minimal unwanted side-effects.
It is more difficult to repair damaged hair than to use gentler techniques that result in less damage to your hair.
Some cosmetic products are partially beneficial in repairing damaged hair but normal quality of hair will return only after the production of new hair to replace the damaged fibers.
Factors that damage hair include the normal "weathering" that occurs to the ends of long hairs that have been exposed to the environment for many years or exposure to chlorine from swimming pools.
The apparent lightening of hair color noted to occur with individuals who have prolonged sun exposure during the summertime is an example of photochemical damage. As with other forms of damage, full reversal is often not possible.
Too Much Zinc May Damage Your Hair
Studies have found that ionic zinc can inhibit 5-alpha reductase (type I) but zinc has no effect on type II reductase. Some studies have found that the combination of B6, zinc salts and azelaic acid, even at low concentrations, caused a 90% inhibition of 5-alpha reductase activity - but this is still not hair growth.
In some persons zinc salts are often used in disorders related to excess DHT such as acne and prostrate hyperplasia. The topical application of zinc has shown to reduce sebum production and acne.
Some people suffering from acne have been found to have zinc deficiencies in their skin, despite of the fact that they have normal levels within their bloodstream.
The effects of topical zinc on hair growth may be due to skin irritation actions. In the 1970's, a number of severe skin irritants, such as nitrobenzene derivatives, were investigated for hair growth properties. While they initially stimulated hair growth, they ultimately produced unacceptable scalp damage and irritation and could not be continued for use.
Zinc salts can inhibit the action of the immune system macrophages on the skin. Since the macrophages are key cell responsible for skin repair, excessive use of zinc salts on the skin could inhibit skin and hair follicle repair. Mulhern et al 1986 reported that excessive dietary zinc in mice reduced plasma copper and induced alopecia. Lansdown 1991 (Westminster Medical School, Department of Comparative Biology, London, UK) examined the dermal irritancy of six zinc compounds was examined in three animal models.
In open patch tests involving five daily applications, zinc chloride (1% aqueous solution) was severely irritant in rabbit, guinea-pig and mouse tests, inducing epidermal hyperplasia and ulceration; aqueous zinc acetate (20%) was slightly less irritant. Zinc oxide (20% suspension dilute Tween 80), zinc sulphate (1% aqueous solution) and zinc pyrithione (20% suspension) were not overtly irritant, but induced a marginal epidermal hyperplasia and increased hair growth.
Thus, hair growth effects observed with zinc may be secondary to dermal irritation. (Lansdown AB, Interspecies variations in response to topical application of selected zinc compounds, Food Chem Toxicol 1991 Jan; 29 (1): 57-64)
Like zinc, topical cortisone has been used to promote hair growth and is often reasonable effective in persons with inflammatory scalp conditions.
But cortisone stops skin repair and, if used for an extended period, ultimately thins the skin, damages hair follicles, and causes hair loss.
Hair Follicles as the Source of Hair
Hair is produced from a skin structure called the hair follicle. The root of the hair is located within the base of the bulb-like follicle.
The follicle is very metabolically active producing hair shafts and is supplied with rich nutrients and growth factors through small blood vessels.
The hair follicle is closely associated with clusters of fat cells which seem to support the health of the follicle.
Baby hair begins to grow around the third month after conception within the womb of the mother. Hair follicles develop as the fetus grows, producing downy hairs (vellus hair) several centimeters long when the baby is born.
After birth, vellus hair in the head is converted into the thicker, longer shafts of 'terminal hair" or what we consider normal of the head. During wound healing, the new skin cells appear to arise from the hair follicle.
Follicles can naturally switch back and forth from vellus hair to terminal hair. This raises the possibility that the vellus hair of baldness could be reconverted back into terminal hair with the proper biochemical signals.
Few new hair follicles are made after birth but the skin contains undifferentiated stem cells that might also be transformed into new follicles with proper biochemical signals.
Three Stages of the Hair Growth Cycle
Your hair follicle adheres to a genetically programmed schedule that includes growth, resting and hair shedding, then the regrowth of new hair.
During its lifetime, a human hair goes through three stages:
Stage 1 - Anagen
Scalp hair follicles enter the hair growth phase and synthesize hair for a period of 2 - 5 years at a rate of about 6 inches (15 cm) per year. Thus a hair 2 feet (60 cm) in length would be about four years old at the end, and only a month or so old near the scalp.
In general, 85% of the scalp hair is in the anagen phase. Eyelash follicles, and the follicles for hair on your arms and legs, have a growth stage lasting only a few months, the resultant hairs that they produce are short.
Stage 2 - Catagen
This is a short transitional stage, The follicle becomes physically smaller as the lower portions of the follicle are absorbed by the body, and ceases to make hair.
Stage 3 - Telogen
A resting stage lasting two to four months, after which it sheds the hair shaft. Only 15% of your hair is resting at any one time. The hair follicle relaxes its hold on the hair shaft bulb, and the bulb of the hair shaft moves closer to the surface of the skin.
Over time the hair shaft loosens and eventually the hair is shed. At the end of the resting stage, the old hair falls out, the follicle enlarges, and a new growth cycle starts and a new hair shaft begins to grow.
Hair Follicles and Area
Hair follicles have specialized cells that have receptors for certain types of hormone messages, when the hormone binds to the cell, the cells respond to according to their innate genetic instructions.
However, some hair follicle cells are programmed differently than others in other parts of the body. In men there are three basic types of hair follicles. A hair follicle on the chin of a young man will begin to grow thick terminal hair as male sexual hormones increase at puberty.
A second type of follicle located on the man's scalp at the hairline is pre-programmed, when it receives the increase of male hormones at puberty, to start spending more time resting and less time growing thick new hairs.
This second type of follicle will contribute to a receding hair line, the stage of male pattern hair loss.
A third type of follicle, located on the back and the sides of same man's scalp, has a genetic program that is unaffected by the male hormone message after puberty.
This type of hair follicle continues its normal cycle of growth, rest, shedding the old hair, and then starting another cycle of growth. It will continue this cycle for many decades.
The innate genetic programming of hair follicle is the reason that hair restoration surgery works. Hair restoration surgeons select hair follicles from scalp areas that have a genetic predisposition to continue growing new hairs, such as the hairs on the side and back of the head.
They move these third type of hair follicles to areas on the scalp where the hair follicles have been programmed to cease hair growth when exposed to male hormones.
The location on the scalp does not affect the genetic programming of the relocated follicles, since the genetic program is dominant over other factors and they continue to grow hairs in the new location.
Creating New Hair Follicles
In a 1998 report, scientists at the University of Chicago's Howard Hughes Medical Center explained how they were able to transform normal skin cells of mice into hair follicles.
Many researchers in wound healing have observed such changes in the past, but never have found the precise signal factor for this transformation. The University of Chicago researchers found that a protein called beta catenin is able to convert normal skin cells into hair follicles.
The message for this protein was successfully introduced into the skin cells of mice and this converted the cells into hair follicle cells and produced very hairy mice.
In the future, it may be possible to genetically introduce the genes for beta catenin into your scalp where hair is not growing well.
Genes can be carried into cells with harmless viruses and such effects are usually well localized. This breakthrough should reach clinical use within 10 to 15 years.
