Cutting a strand of hair across the width of its diameter will give a cross-sectional picture of the hair shaft and, apart from showing its distinctive racial type, will also exhibit three distinct zones of physical differentiation.
On the outside is the cuticle. This is composed of a layer of very flat, thin, dead cells that overlap one another, much like the tiles on a roof. They are coated with an extremely thin layer of a hard, waxy substance only a few molecules deep. This natural coating causes the cuticle layer to repel water and is especially effective in ulotrichous hair. The effect is augmented by further secretions from the sebaceous glands coming from inside the follicle.
When the cuticle’s ‘tiles’ are laying down flat, the hair is smooth and shiny; however, some hair treatments can cause these tiles to lift up. Treatments that have decidedly high pH levels (that are alkaline, in other words) are notorious in this respect. Once this has happened, the hair becomes rough, dull and much more easily tangled as the uplifted tiles of one strand mesh into the uplifted tiles of another. Pulling a comb or brush through such hair can damage the already weakened shafts even further and will cause considerable pain. In some severe cases, the only option is to cut the truly matted hair back to just above skin level. This applies to animals as well as humans.
The next layer is the called the cortex, and it is this layer that provides the hair with its strength, thickness and colour. Only here are intra-cellular grains of the two pigments found, as well as bundles of keratin rods. Although this cortex layer absorbs water quite well the keratin itself within it is insoluble.
Keratin is a supremely tough structural protein that, in hair, organises itself into microscopic filaments made up of aligned bundles. Laid end to end to form spiral plaits, these keratin rods impart huge strength to various physical structures within the animal kingdom. Keratin makes up not only our hair and nails, but also sheep’s wool, bird beaks, animal claws, rhinoceros horns, bird feathers, tortoise shells, hedgehog spines and elephant tusks, to name but just a few of them.
Keratin does have a weakness, however. It is a protein and is, therefore, susceptible to being used for food by other organisms. Fungal infections on the skin like athletes foot and ringworm (Tinea pedis and dermatophytosis respectively) occur because the fungi involved do exactly this. They actually break the keratin down and feed upon it.
The innermost layer is called the medulla. In some people’s hair, this area is simply an empty space. In others it contains a loose, disorganised mass of weak and mostly disconnected cells. From the outside, it is impossible to tell whether the medulla in any particular strand of hair is empty or not. Either way, it appears not to make much difference to anything.
Chapter Seven
Sebum
Sebum is a word that comes from the Latin for tallow (animal fat). Sebum itself is the ‘oil’ that is continually secreted from the sebaceous gland attached to the follicle of terminal hairs. This oil gets discharged into the follicular canal and then seeps out from it over the skin and up the hair shaft. Grooming behaviour in both animal and humans is designed to ensure the greatest distribution of this oil. Sebum keeps the skin and hair both water-repellent and moisturised. It does this by acting like a waterproof barrier over the skin, keeping internal moisture within the skin layers and keeping external water away from the epidermis itself. Coupled with the sweat glands, sebum turns the skin into a tightly controlled, semi-permeable membrane.
Sebaceous glands and the follicles cover virtually the entire body but are concentrated on the face and scalp as well as the inner surface of the ear canals. They are always absent from the lips, the palms of the hands and the soles of the feet, however.
Although an oil-based secretion, sebum’s formulation differs depending upon its location and, more importantly, its function at that location. Earwax (also called cerumen) is largely composed of sebum, for instance, as is the far more fluid and colourless oil that is secreted across the surface of each eye. This oily film floats on the top of the tear fluid itself to prevent its too-rapid evaporation.
The composition of sebum can be easily altered in this way because it is not a single chemical substance at all; it is actually composed from an assortment of them. ‘Normal’ sebum contains water, triglycerides, fats, waxes, squalane and various other substances including natural antibiotic enzymes, vitamin E (a fat-soluble antioxidant) and pheromones. By simply varying the proportions of these components the various types of sebum ranging from the heavy waxes to the far lighter tear-oil are arrived at.
Sebum itself is odourless and what we think of as its characteristic smell is actually one brought about through both its oxidation and the action of bacteria and fungi (yeasts) feeding upon it. This bacterial action, in particular, is also a prime cause of acne.
Sebum has always been believed to be somehow involved in hair-loss. Its exact position within the chain of events, however, depends upon what you believe the principal causative agent to be. The nature of these causative agents is discussed later. Suffice to say that the reputation of sebum as some sort of necessary nuisance is entirely undeserved.
Chapter Eight
Hair Growth
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