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Everything You Should Know About Hair


  • The average person is born with about 100,000 hair follicles on the scalp.
  • Redheads have less (about 80,000) and blondes more (about 120,000).
  • Each hair fiber is manufactured by a single follicle, located about one-quarter inch beneath the skin.
  • On cross section, an Asian hair fiber is perfectly round, while a Caucasian hair is oval.
  • The more oval the cross section, the greater the hair’s waviness.
  • Average hair is 70 microns in diameter. Fine hair is 60 microns, while coarse hair is 80 microns.
  • The caliber or diameter of the hair is determined at conception.
  • In the absence of pattern balding-thinning, almost all hairs are the same diameter and equally distributed on the scalp surface.
  • Hair diameter is critical. Someone with 100,000 coarse hairs will have twice the hair (by weight) as someone with 100,000 fine.


  • Each follicle on the scalp goes through a predictable cycle about every 4 years. An 80-year old follicle has had about 20 life cycles.
    • Anagen phase – The follicle produces hair for about 4 years, then enters telogen phase.
    • Telogen phase – The follicle stops making hair for about 4 months, then enters catagen phase.
    • Catagen phase – The hair falls out, or is pushed out by the newly emerging anagen hair.
  • During anagen, scalp hair grows at one half inch per month.
  • Hairs in telogen can be painlessly plucked. Anagen hairs are well-anchored.
  • If uncut, scalp hair will generally grow to waist length.
  • With normal synchronized turnover, it is normal to shed 50 to 100 scalp hairs each day.
  • An uncommon genetic variant is continuous anagen. Scalp hair has been documented to be over 18 feet. (A Chinese woman in Guinness Book of Records – 2004).
    • In the animal kingdom, a variant (of this variant) is called angora. It can be present in cats, rabbits, etc.
  • On the scalp, a high percentage of hairs are in anagen phase, and a small percentage in telogen. Their anagen phase is long and their telogen phase is short. The opposite is true of hairs on the arms, legs, and eyebrows (see below).


  • In balding, a progressive reduction in diameter will result in an eventual reduction in density.
  • This hallmark of balding cannot be seen with the naked eye or photos in its early stages.
  • Microscopic scalp exam will only identify diameter reduction. It will not quantify diameter reduction.
  • CST (cross section trichometry) can simultaneously measure hair diameter and hair density.
    • CST is an instrumentation used in the hair research labs of L’Oreal, P&G, and Unilever.
    • It can detect a 2% change in hair growth or loss with an accuracy of 95%.
    • It is the only way to scientifically determine HOW MUCH HAIR is present.
  • At Hevia Hair Science, we perform CST measurements on every patient… on every visit.
  • Length is not measured when determining HOW MUCH HAIR, because length varies with styling.


  • Eyebrows, arm, and leg hair populations are proportioned differently and cycle differently.
  • A high percentage of these hairs are in telogen phase; a small percentage are in anagen phase.
  • Their telogen phase is long and their anagen phase is short. (That’s why eyebrows don’t grow inches and in front of your eyes!)
  • A plucked eyebrow hair (most are in telogen) will convert to anagen and grow a new hair quickly with a soft tapered tip.
  • A shaved eyebrow hair (most are in telogen) might take 6 months before it cycles through anagen again.
  • Shaving hair does not make it grow faster or thicker. The follicle (growth center) is well beneath the skin surface.
  • The unshaven hair has a soft tapered tip which is much more flexible than its proximal shaft.
  • The cut hair, squared off at the cut, has lost its tapered tip and behaves stiff and stubbly. (This why salons pluck, thread, and wax eyebrows… rather than shave or cut.)


  • Pattern balding-thinning occurs in both men and women.
  • Pathology: The follicle and its hair become progressively reduced in diameter (miniaturized).
  • In one square inch containing 1000 normal hairs, there is no visible underlying skin.
  • In one square inch containing 1000 miniaturized hairs, the underlying skin can be seen.
  • Progressive miniaturization occurs on top of the head and spares the back and sides.
  • On scalp micro exam of the back and sides, essentially all hairs have a normal diameter.
  • On scalp micro exam of the top, there is wide range of fine, intermediate, and normal diameters.
  • One must lose 50% of his/her hair (by weight) before the underlying skin is visible.
    • Translation: You’ve lost 50% of your hair before you realize that you’re balding!
    • Therefore: scalp photography will detect changes, only if the loss is more than 50%.
  • CST can detect and measure balding, regardless of its severity stage. Photography CANNOT detect or measure balding if the balding is early and less than 50%.


  • Full-sized hairs do not “fall out.” They become progressively finer or “thinner.”
  • With each cycle, the follicle becomes smaller, and the hair diameter becomes finer.
  • Thinning hairs are shorter because they grow for a shorter time before they recycle.
  • Eventually they become very fine, short, and fuzzy. They grow for only a few months.
  • Ultimately the miniaturizing follicle disappears and a smooth “bald” hairless area is apparent.
  • Once the diagnosis of pattern balding has been established, miniaturization will progress 100% of the time… sometimes slowly, sometimes rapidly, but it will not self-correct.
  • As long as a reduced-size follicle remains, most medical hair loss treatments should work.
  • Once the follicle has vanished, the hair can only be replaced by transplantation.
  • The earlier the treatment is started (before the follicles vanish), the better it works.





  • By age 60: 25% of men have minimal loss, 50% have mild-moderate loss, and 25% have a severe loss (at worse, little more than a horseshoe fringe). Therefore, 75% of healthy men are actively balding.
  • The disorder is genetically determined; It is not predictable whether or not a man will lose his hair.
  • However, the severity of the loss is usually foreshadowed by the men on the mother’s side.
  • Balding is typically not related to stress.
  • On the other hand, gray hair and generalized shedding, are sometimes related to stress.


  • 35% of perfectly healthy women have thinning to a mild degree.
  • It is not unusual in related grandmothers, mothers, sisters, and aunts.
  • Ten percent of the affected women might have a correctable endocrine abnormality.
  • Unlike men, the frontal female hair line does not recede as balding progresses.
  • As in men, the back and sides are spared.
  • Thinning in women rarely advances to the stage of complete hair loss.
  • Breakage is common because the highly miniaturized hair population is easily traumatized by styling, tangling, brushing, curlers, heat devices, and salon chemical processing.


  • Shedding is much more common in women than men.
  • It should not be confused with thinning, in which the loss spares the back and sides.
  • Shedding is characterized by a somewhat abrupt hair fall over the entire scalp.
  • The follicles remain healthy and full-sized, but the hair in many follicles is lost.
  • On surface scalp examination, the hairs are not miniaturized; they are full-sized, but there are fewer per square inch.
  • Shedding occurs when the synchronization of the anagen-telogen cycle is disrupted.
  • During pregnancy or while taking contraceptive pills, almost all scalp hairs convert to, and remain in, their anagen phase. Very few hairs are shed daily.
    • Upon delivery, the anagen telogen ratio returns to normal; and months later, a significant shedding event takes place.
    • This shedding is called telogen effluvium and usually occurs 4 months after a high fever, delivery, contraception pill discontinuation, general anesthesia, severe weight loss, etc.
  • Low-grade, non-cyclic shedding (in distinction to telogen effluvium) can be caused by thyroid abnormalities, low Vitamin D, low serum ferritin, anemia, malnutrition, immune deficiency, cancer, auto-immune disorders, physiologic imbalances, etc.
  • Shedding almost always self-corrects over several months… when the abnormality is treated or the physiologic event has passed.
  • The regrowth that follows shedding from cancer chemotherapy varies with the drug and the duration for which it was taken. It is called anagen effluvium.
    • By chilling the scalp skin during agent infusion, the scalp vessels constrict. Less chemo-agent reaches the susceptible follicle, and anagen effluvium is less likely to follow.


  • A genetic variant of hyper-density (over 120,000 scalp follicles) can sometimes occur.
  • These women and their stylists remark that the hair is abundant, beautiful, and difficult to cut. They simply have more than the normal amount of scalp hair.
  • Young women with hyper-density will begin normalize, by shedding, as they reach adulthood.
    • To their dismay, they lose lots of hair as they approach normal density.
    • They are often diagnosed as telogen effluvium, but their medical history is normal.
  • When measured using CST, their density is also normal, in spite of excessive shedding.


  • Fine-haired individuals, and those with miniaturized hairs due to thinning, are most susceptible to breakage and damage.
  • Hair damage in women is most commonly caused by services received in the salon.
    • Culprits include: Dyes, bleaches, highlights, relaxers, straighteners, keratin treatments, etc.
    • Very hot dryers, irons, brushing tangled long and curly hair, fine combs, scalp scrubbing, vigorous towel drying also contribute to breakage.
  • Biotin by mouth (not topically) will make hair stronger and more resistant to breakage.
  • Contrary to common belief, biotin does not cause hair to grow or stop hair from falling.
  • Brittle and dry hair can also be caused by nutritional deficiencies and hypothyroidism.
  • Nutrients or biotin by mouth will only strengthen the newly emerging portion at ½ inch per month.
  • Breakage of damaged hair (if not severe) can be minimized by oils, conditioners, detangling agents, surface-smoothing agents, and gentle hair handling.
  • When re-coloring with dyes, only the roots should be colored.
  • Hair-damaging processes are rarely follicle-damaging.
    • The salon service must significantly irritate or damage the scalp skin (with follicle injury) in order to cause permanent loss.


  • The major categories of medically-proven treatment include minoxidil, laser, finasteride, PRP, and hormonal-influencing drugs.
  • Minoxidil is available over-the-counter in 2% and 5% strengths, in liquid and/or foam preparations as brand name Rogaine or generic.
    • Deeper penetrating minoxidil can be compounded by our pharmaceutical chemist.
  • Laser light devices are available for home use in the configuration of brush, helmet, or crescent band style. No prescription is required.
    • The laser light works by penetrating the skin.
    • Laser rays will bounce off the hair.  The more hair that is present, the less efficiently they deliver follicle-stimulating light.
  • Finasteride (for men only) is a prescription. Although quite effective, it has several side-effects. It is available in the brand name Propecia and in generic.
  • Platelet Rich Plasma (PRP), also quite effective, is performed in the office and takes approximately 1 hour.
    • A small amount of blood is drawn and centrifuged. Platelets are collected and condensed, and then injected into areas of hair loss.
    • The platelets contain growth factor. Growth factors stimulate the dormant miniaturized follicles to re-enter their anagen phase.
    • If you are receiving PRP treatments, it’s important to not take aspirin, Advil, Aleve, NSAIDs, or steroids for one week before and three weeks after the PRP treatment.


  • Because continuous treatment is required, the safety, convenience, cost, and efficacy are all considerations to be discussed with the physician.
  • OTC minoxidil 5%. Dosage is twice a day.
  • Enhanced minoxidil 5%. Dosage is once a day.
  • Laser light. Dosage depends on the configuration of the device.
  • Finasteride. Dosage is 1 mg per day. Higher doses work no better and cause more side effects.
  • PRP. If used as the only treatment, dosage is 4x per year.  When used in addition to one of the above treatments, PRP can be administered less frequently.
  • Biotin dosage is 5 mg twice a day.
  • Nutritional supplements will improve hair quality, but none contain sufficient amounts of biotin.
  • In general, females should not be treated with finasteride. Its safety in women has not been well-established.
  • Finasteride is absolutely contraindicated in pregnancy. Pregnant women should not even touch broken pills. Anatomic malformations of a male fetus can occur during later stages of pregnancy.
  • It is safe for pregnant women to have intercourse with men taking finasteride.
  • Minoxidil is contraindicated during pregnancy and breast-feeding.
  • Be sure to tell your primary physician if you are taking biotin or finasteride.
  • Biotin will interfere with several blood tests performed by the laboratory.
  • Finasteride will falsely lower the PSA about 50%. PSA is a screening test for prostate cancer.


  • All accepted treatments affect the dormant, miniaturized follicle in a similar manner. However, each works through a somewhat different metabolic pathway.
  • Some treatments are more effective than others.
  • Shortly after treatment commencement, almost all scalp hairs are converted to their anagen phase.
  • The dormant hairs in telogen phase are converted to anagen, and present visually as “more hair.”
  • A small percentage of hair falls out before entering anagen, so a brief period of shedding occurs.
  • This is a positive sign, not a reason to stop treatment. It means the treatment has successfully influenced the anagen-telogen synchronization.
  • While held in anagen, the follicles will not recycle and will no longer miniaturize.
  • The short, miniaturized hairs become long miniaturized hairs.
  • Eventually, their miniaturized diameters become larger and approach normal.
  • It should be emphasized that success is not guaranteed.
  • In advanced cases of thinning, some patients respond poorly or not at all.
  • If the follicle is no longer present, there is nothing for the treatment to work upon. There must be some fine hair on the scalp surface for treatment to succeed.
  • Obviously, the earlier the treatment is started, the more effectively it works.
  • If any of the treatments are discontinued for more than a few weeks, the positive effects of the treatment will be lost.
  • If treatment is discontinued for a longer period, the follicle which was kept active by the treatment will resume miniaturization and, if very small, might vanish completely.
  • Treatment is essentially forever… or until something new and better comes along.


  • Hair transplant surgery is designed to replace the vanished follicles.
  • Bits of skin containing hair are taken from the permanent fringe in the back and sides.
  • No new hair is created. It is simply moved to a new location on the scalp.
  • 50% of the hair can be removed from the donor fringe before it becomes visibly obvious.
  • The small grafts are planted in hairless areas or between the existing original follicles.
  • Transplanted hair will grow forever. Follicles from the fringe do not miniaturize.
  • Transplanted hairs DO NOT require medical treatments to keep them growing, however…
  • Original hairs DO require continued medical treatment, or they will be lost.
  • When hair transplants are performed on patients with partial hair loss, medical treatment must be maintained. Otherwise, the original, non-transplanted hair will continue to miniaturize.
  • Hair cloning is reserved for hair transplant patients who have surgically transplanted the maximal amount of hair from the donor fringe.
  • Cloning is presently at a laboratory research level.


Additional Resources

Hevia Hair Science
Q & A: Pattern Baldness & Thinning


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