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Dr. Desmond Tobin, professor of cell biology from the University of Bradford in England, suggests that the hair follicle has a “melanogentic clock” which slows down or stops melanocyte activity, thus decreasing the pigment our hair receives. This occurs just before the hair is preparing to fall out or shed, so the roots always look pale. Moreover, Dr. Tobin suggests that hair turns gray because of age and genetics, in that genes regulate the exhaustion of the pigmentary potential of each individual hair follicle. This occurs at different rates in different hair follicles. For some people it occurs rapidly, while in others it occurs slowly over several decades.In a February 2005 Science article (Nishimura, et al.) Harvard scientists proposed that a failure of melanocyte stem cells (MSC) to maintain the production of melanocytes could cause the graying of hair. This failure of MSC maintenance may result in the breakdown of signals that produce hair color. There are other factors that can change the pigmentation of hair, making it lighter or darker. Scientists have divided them by intrinsic (internal) and extrinsic (external) factors:Intrinsic factors:Genetic defects Hormones Body distribution Age Extrinsic factors:Climate Pollutants Toxins Chemical exposure Hair-raising facts:An average scalp has 100,000-150,000 hairs.Hair is so strong that each hair can withstand the strain of 100 grams (3.5 ounces). An average head of hair could hold 10-15 tons if only the scalp was strong enough!Human hair grows autonomously, that is each hair is on its own individual cycle. If all our hair were on the same cycle, we would molt!Hair has the highest rate of mitosis (cell division). An average hair grows 0.3 mm a day and 1 cm per month.
Hair Turns White OvernightListen to Karl talk about Hair Turns White Overnight(You will need Real Audio which you can download for free)Paul rang in and asked, "How could someone's hair turn white overnight?" I told him it wasn't possible, but I've since discovered that I was actually wrong. It's because of a skin disease called alopecia areata. The hair can't actually turn white overnight, because all the hair is "dead", and the only way you can make its colour change is with dyes. Hair gets its colour from a chemical called melanin, which is pumped in by cells at the base of the hair follicle. As your hair goes grey, these cells at the base stop making melanin. So some hairs will be their normal colour, but some (the ones without melanin) will be completely white. So here's a great truth - there's no such colour as grey hair. Grey hair is dark hairs, with the newer white hairs mixed in. So how can somebody's hair turn white overnight? Easy, they first have grey hair (which is actually the mix of dark hair and white hair) - and then all the dark hair falls out over a few days. This could be caused by a disease called alopecia areata , where your hair, for no apparent reason, simply falls out. Unlike common balding, alopecia areata is just as likely to happen in women as in men. So if you've got grey hair, and those few remaining dark ones bail out, bingo - instant white hair! It can't happen overnight, but it can happen...
Thank You Paul,very interesting stuff !If I had white hair and then had a shock...what would happen then ?