From an old thread..interesting..anyone know if it's accurate?
Seasonal hair shedding
We, and much of the mammalian world, have two main shed seasons. The biggest shed occurs in early autumn and a smaller one in spring. Essentially we are replacing our summer coats with winter coats. Perhaps the best example is the arctic fox that sheds a pigmented summer coat and replaces it with a white coat (camouflage) for winter conditions. Much of the research on seasonal shedding and hair regrowth is conducted with mink (some studies from Australia on sheep and goats too). Researchers have looked at prolactin and melatonin levels among other factors as a potential regulator of the changes in hair growth. Giving mink melatonin, or reducing exposure to daylight, promotes shedding of the summer coat and the onset of the winter anagen growth stage. Possibly it is a similar situation for humans where changes in daylight hours modify the melatonin secretion rate from the pineal gland and this in turn affects hormones and/or their receptors in the skin.
The shed cycle in humans has not been investigated in much detail, but a few studies from the UK demonstrate the seasonal shed cycles. Although there is an increase in shedding during spring and fall, the number of hairs shed still falls within the generally recognized limits of 50 to 100 hairs a day. So in spring and fall the daily shed rate may be closer to 100 hairs a day and in summer and late winter the typical shed rate is closer to 50 hairs a day. However, the average rate of shedding does vary from person to person. Some people can be high shedders, but also have high rates of hair growth and replacement so they have no net hair loss. To understand your own seasonal hair shedding it is better to compare the hair shed rate in spring/fall to summer/winter within yourself rather than compare it to other people. Whether there are still seaonal shed cycles for humans living at the equator is not known - I would guess not if the changes are due to melatonin levels.
