Hair follicles on the scalp do not continuously produce hair. They cycle through a growth stage for up to two or more years, then regress to a resting stage for up to two months before going into a fallout stage with the beginning of a new growth cycle. At any time on a healthy human scalp 80-90% of the hair follicles are growing hair. That leaves 10-20 % of scalp hair follicles in a resting or fallout state called telogen.
When the body experiences a “shock,” whether it is emotional or physical, (such as rapid weight loss, hormonal changes after childbirth, accident, operation, or loss of a loved one) a larger percentage of hair remains in the fallout phase and diffuse thinning of hair on the scalp occurs. Handfuls of hair (the hair has a small “bulb” on the end) are often noticed in the shower or on a comb within two months of the initial “shock.” People with this type of hair loss, also called Telogen Effluvium, never completely lose all their hair, but the hair can become noticeably thin in severe cases. While hair loss is often limited to the scalp, in more serious cases the hair loss can affect other areas, such as the eyebrows or pubic area. This form of hair loss usually lasts less than six months and the affected individual has a normal scalp density again within a year.
The good news is that in most cases the hair loss is fully reversible. The hair follicles are not permanently affected; there are just more hair follicles in a resting state than usual.
Chronic stress and diet deficiency can lead to persistent hair loss. There does seem to be a link between stress and changes in hair follicle biochemistry.
In first world countries the average diet is usually sufficient in vitamins and minerals. In North America we do see diets deficient in iron (or low iron) related to menstruation in women. Vitamin D deficiency can occur due to lack of sunlight. Other potential deficiencies in the North American diet – such as lack of Zinc, L-lysine, vitamins B6 and B12 – have also been linked to hair loss. If a dietary deficiency appears on a blood test, then supplements can work. A deficiency in thyroid hormones can be treated with hormone supplements.
However, often a specific causal factor can not be identified. If this is the case, a pharmaceutical called Minoxidil can be prescribed that is a direct hair growth stimulator. If the underlying cause is not corrected, then minoxidil must be continued to block re-development of hair loss. With removal of the trigger, minoxidil can be stopped.
Everyone naturally sheds hair, and you may see more hair shed at certain times of the year. Studies have shown that humans living in Northern Europe shed more hair in the fall and to a lesser extent in the spring. It has been suggested that hair shedding is probably due to changes in hormones in response to changes in daylight exposure. Such hair loss should be temporary.