some six to ten weeks later. Many alcoholics have poor hair growth or even hair loss because their way of life tends to lead to malnutrition.
  Some minerals may be particularly important for hair growth. For example, some people who lack zinc in their diet produce only fine, sparse hairs and even lose their hair. Vitamin B, also known as panthenol, plays a part in hair growth. It also improves the physical properties (elasticity, strength and gloss) of the hair shaft.
  The hair cycle for each individual hair is influenced by the levels of various hormones in the blood. Thyroid hormone speeds up growth in resting hair follicles. Steroids taken by mouth slow it down, though steroids inhaled for the treatment of asthma do not affect hair growth.
  The hair of the scalp is, however, most sensitive to the effects of male hormones (androgens), which are in the blood of people of both sexes (only in different proportions in men and women). Androgens are the most important factor regulating hair growth, and also the thickness of the hair shaft. Female hormones (oestrogens), which both sexes have too, slow down hair growth during the growing period but also make that period longer. Many

women notice a difference in their hair growth during pregnancy. At this time women have vast amounts of oestrogen in their blood, far outweighing their male hormones. It is the balance between the male and female hormones which decides the growth of the hair.
  We have already seen how at puberty the immature vellus-like hairs on our bodies can change to terminal hairs. This change results from the dramatic rise in androgen levels at that time. It is especially noticeable in young men. Young women who suffer from the condition of anorexia nervosa, however, stop having periods and produce very little oestrogen: their natural androgens tend to thicken their fine vellus-like hairs in the same way.
  The effects of androgens continue long after puberty. Some areas of the skin respond to these hormones more vigorously
than others do, and at different times of life. Pubic and armpit hair begins to grow at or soon after puberty. Most men's beards do not grow strongly until the owners reach their thirties. The growth of chest hair reaches a peak even later, and hair in the nose and ears grows most in late middle age.