Facts of life Silver among the gold [Archives:2005/865/Health]

August 4 2005

By Dr. Khaled alNsour
For the Yemen Times

People around the world have several hair colours, black, brown, blond and even red. But eventually when people grow old whatever their initial hair colour was, it starts becoming grey until finally turns white. This change in the hair colour is because of the alteration of gene expression or the loss of certain pigments.

Our genes determine everything including when we grey and how white our hair will become. Caucasians grey earlier than Asians. We grey because our hair loses pigments. As cars and people age, things start going wrong. Greying is one of those things. Often beginning in their 30s, grey hairs start to appear because hair shafts contain less melanin, the pigment that colours hair.

The colour-producing cells (melanocytes) gradually disappear for some unknown reason. For a hair to have colour ) its root hair bulb must contain melanocytes actively making pigment and transferring the colour to the hair shaft.

Melanin produced by epidermal melanocytes protects human skin by screening harmful ultraviolet radiation. However, the biologic value of hair pigmentation is less clear. In addition to important roles in social/sexual communication, one potential benefit of pigmented scalp hair in humans may be the rapid excretion of heavy metals, chemicals, and toxins from the body by their selective binding to melanin. The primary distinguishing feature of follicular melanogenesis, compared to the continuous melanogenesis in the epidermis, is the tight coupling of hair follicle melanogenesis to the hair growth cycle. Each hair cycle is associated with the re-construction of an intact hair follicle pigmentary unit at least for the first 10 cycles or so. Thereafter, grey and white hairs appear, suggesting an age-related, genetically regulated exhaustion of the pigmentary potential of each individual hair follicle.

As people age, their hair bulbs become an “increasingly hostile place” for melanocytes to work properly and eventually these cells lose the battle and die, says Desmond J. Tobin, reader in cell biology at the University of Bradford, England.

Other parts of the hair follicle try to replace the cells with new melanocytes but usually the efforts fail. Consequently, the bulbs gradually run out of melanocytes. The hair gets greyer and greyer until, finally, the hair bulb has no melanocytes to make pigment and the hair becomes melanin free. Then the intrinsic colour of the protein (keratin) that makes up the hair strand is revealed. It's the same colour as the keratin in our fingernails and toenails ) an off white. Our hair looks white.

While the perception of “grey hair” derives in large part from the admixture of pigmented and white hair, it is important to note that individual hair follicles can indeed exhibit pigment dilution or true greyness. This dilution is due to a reduction in tyrosinase activity of hair bulbar melanocytes, sub-optimal melanocyte-cortical keratinocyte interactions, melanocyte death, and defective migration of melanocytes from a reservoir in the upper outer root sheath to the pigmentation-permissive microenvironment close to the follicular papilla. Importantly, melanocytes taken from grey and white hair follicles can be induced to pigment in vitro. Melanocyte aging and death may be associated with reactive oxygen species-mediated damage to nuclear and mitochondrial DNA with resultant accumulation of mutations with age, in addition to dysregulation of anti-oxidant mechanisms or pro/anti-apoptotic factors within the cells. Furthermore, the hair follicle pigmentary unit may be a valuable, highly accessible, model system for the study of neuronal cell aging and neurodegenerative disease. This is supported not only by significant melanocyte and neuronal cell relatedness, but also by the observation that hair follicle melanocyte deletion, after prolonged exposed to melanogenesis-related and keratinocyte metabolism-related oxidative stress, is likely to utilize similar pathways to those utilized by aging/degenerating neuronal cells. Thus the study of age-related changes in the hair follicle pigmentary unit may provide insights into aspects of human health and well-being beyond basic hair colour considerations.