Normally, about 90% of our scalp hairs
are growing and 10% are resting. The resting hairs stay in place
for several months, but when a new hair is formed and begins its own
growth cycle, the old one is pushed up and out. We normally lose
50 - 100 scalp hairs per day as old hairs are shed to make room for
Many events can cause a definite change
in the hair cycle. A temporary increase in the rate of shedding
may occur 3 - 4 months after childbirth, or following a high fever,
major illness, major surgical procedure, blood loss, or severe
emotional stress. It has also been seen recently in association
with rapid weight-loss diets involving severe restriction of calories
(less than 800 per day) or protein. In these situations, hair
will literally come out by the handful, but it always regrows some
months later. Various drugs can also cause hair shedding.
In other instances, hair loss is not increased but replacement is
inadequate. This can occur as a result of thyroid disease,
cancer, iron deficiency, and some cases of diabetes.
So-called "male-pattern" hair thinning,
the all-too-familiar receding hairline seen earliest at the temples
and over the top of the scalp, is very common in men. It may
also occur in women, in whom it normally appears 15 - 20 years later
than in their male relatives. The age of onset, degree of
thinning, and ultimate hair pattern are determined by male hormone
(androgen) stimulation and by heredity. In other words, the
eventual development of male-pattern thinning is a normal and
inevitable response to the same stimuli (androgen) which promote
normal sexual development. Although seborrhea (oilness) and
dandruff are sometimes associated with this type of hair loss,
treating these conditions does not influence the regrowth of hair.
In women, genetic hair thinning is more
difficult to diagnose with certainty at an early age, but it seems to
be quite common. The hair loss is more diffuse and less
patterned. If one can exclude other common causes of hair loss,
if there is a family history of the condition, and if the onset is
gradual and not associated with irregular menstrual periods or
excessive growth of hair elsewhere on the body (hirsutism), it is
likely that this hair loss is a normal event.
Familial (or genetic) hair thinning has
never been shown to be helped by local applications or injections, by
radiation, or by any other physical treatment in either sex.
There are no foods or vitamins which will specifically help hair
growth, though food health and nutrition are generally important.