Читать книгу Reversing Your Hair Loss - A Practical Scientific Guide - Robert J. Hall - Страница 12

In general terms, each hair is roughly one 500th of an inch thick for most cymotrichous blondes. At the other end of the spectrum, the average strand of lissotrichous hair found on any Japanese boy’s head could be anything up to four times thicker. These figures will obviously vary between individuals, but the general picture remains true.

The number of hairs on any particular scalp will also vary. An average figure would be somewhere in the region of 100,000 in total for lissotrichous individuals. Ulotrichous hair is a lot less dense than this. The greatest variation in hair density, however, occurs amongst cymotrichous individuals. Within this class of individuals are to be found both the highest and lowest number of individual scalp hairs. Redheads generally have the fewest number; the figure generally given is in the region of 75,000, whilst blondes have the highest hair count at around 140,000.

Healthy, well-nourished hair grows at roughly just over half an inch per month, the general figure usually given is about nine inches per year. However, this figure can only be a very general guide because, firstly, ulotrichous hair grows more slowly than the other two sorts. Secondly, as hair lengthens its growth rate actually slows down. Hair that is over three foot long will only be growing at half the rate it was when it was just three inches long for instance.

It used to be thought that whatever the type of hair, one thing remained constant. The rate of growth depended upon the general climate. This variation was measured and there was found to be an approximate ten percent difference between the summer and winter growth rates. The explanation for this is more complicated than at first thought, however.

The original model had it that during hot weather the circulation to the scalp was increased by the need to radiate internal heat away from the internal organs. This increased circulation brought a greater supply of nutrients to the follicle and this, in turn, gave rise to increased hair growth. The opposite was imagined true during the winter season. The need to conserve heat meant that the blood supply fell and the rate of growth was consequently retarded.

Further research proved that this was not especially true; nor was it a particularly convincing explanation, anyway. Researchers pointed out that headgear has always been readily available to keep the scalp warm. Moreover, the time spent outdoors in cold weather was less than in previous generations. We now live in heated houses, travel in heated trains and work in heated offices. The variation (although much smaller) was also found in subjects working in non-temperate parts of the world.

It was then found that it was cymotrichous hair that went through this annual cycle rather than the other two types. Further research correlated the fact that sperm levels amongst cymotrichous males also rose and fell in the same seasonal cycle, as did their body-fat levels. It was then discovered that the hair in these males went through a barely noticeable, but nonetheless perfectly recognisable, small-scale hair gain cycle starting in the autumn and winter months, with the extra hair falling out in the spring. Basically, what had been discovered was that white males (again, especially Nordics) underwent an annual moult.

Putting all the facts together, it seems that falling levels of light alter hormone production levels and associated enzyme activity which, in turn, triggers hair growth, alterations in sleep patterns, sperm production and fat storage. This is exactly what happens to temperate mammals in winter, of course. They grow winter coats, put on extra body fat and then hibernate.

The initial observations had been restricted to white males living in temperate climates and it was assumed that the phenomenon was a purely mechanical reaction to ambient temperature. It was eventually found that the trigger was light not heat and, far from being a simple reaction to the weather, it was a subtle train of events that were genetic in origin, and hormonal in action.

Going back to how hair grows; in general terms we now know that it is more complicated that it at first seems. Each hair grows out from its associated follicle and eventually rises above the surface of the skin. It does not lengthen continuously, however. This is because each hair grows in a regular fashion that consists of three specific phases that follow one another in a regular sequence. These phases are called the anagen, catagen and telogen phases. Each of these phases has distinct sub-phases within it that also follow in a strict order. This is invariably true whatever the type of hair and whatever the climate.

The anagen phase is one of active growth; around ninety percent or so of your hair is in this state at any one time. The next is the slowing down, cessation and shedding phase, known as the catagen phase. Only one or two percent of your hair is in this phase. The last one is the telogen phase, which consists of resting and dormancy; roughly ten percent of your hair follicles will be in this phase at any one time. In general terms, the hair follicle will go through one complete cycle approximately fourteen times before lapsing into senescent inactivity.

These three phases occur in different hairs at the same time, so one strand may be in the telogen phase whilst its neighbour might still be actively growing. The net result is that the number of visible hairs on the scalp remains roughly constant (seasonal fluctuations amongst the susceptible types notwithstanding) until the balding process starts in earnest.

The hairs on your head go through a complete cycle in about three to four years. Your eyelashes and eyebrows, on the other hand, complete it in less than six months, sometimes a lot less. This is why your eyebrows and eyelashes are always shorter than the hair on your head. They simply do not have as much time to grow long.

Your potential maximum hair length is completely dependent upon the length of its growing phase. This is its limiting factor. Every other factor like nutrition and treatment takes away from the potential maximum length possible for your hair; they never add to it. The only way to make your hair grow longer than this potential maximum is to increase its rate of growth whilst in the anagen phase and/or somehow increase the length of the anagen phase itself. This might be possible. Once the cycle enters into the next phase, however, then nothing can be done until the entire cycle is completed.

At the start of each hair follicle’s new cycle, a new bulb is grown at the site of the previous one. The old one died and fell out at the end of the catagen phase. The process of losing a hair involves the blood supply to the hair bulb simply shutting off and the bulb shrivelling up. The hair shaft with its withered and shrunken bulb is now called a club hair, so-called because of its supposed resemblance to a caveman’s club.

These club hairs are the ones that you lose every day as part of the normal cycle of things; this process is entirely analogous to the way in which trees shed their leaves in the autumn. Autumn comes and the leaves die, but sometimes they still stay attached to the branches they grew on only to get blown off during the first winds of winter. Our hairs do the same; they die and we lose them through brushing or combing as they get detached from their pits and then completely pulled out to appear painlessly in your comb or brush.

The simple fact of the matter is that although we might all be born with hair there is no guarantee that we will all die with it. The next section deals with this sad fact.