Good Hair. Libby Peacock

gives hair its colour. Pigment makes up only about one per cent of a hair, and although there is a wide range of human hair colours, they all derive from only two melanin pigments: eumelanin, a dark pigment predominating in black and brown hair, and phaeomelanin, a light pigment predominating in blonde and red hair. Many people’s hair contains a mixture of the two pigments: the more eumelanin, the darker the hair.

      Each hair has a tiny muscle – the erector pili – attached to it. This muscle contracts when it is cold, pulls the hair erect and causes goose flesh. Sebum, an oily substance secreted by the sebaceous glands in the skin, lubricates the hair, making it waterproof and shiny. As all teenagers discover sooner or later, an excess of sebum leads to greasy hair. Too little of it causes dry hair.

       Thick or thin

      We are all born with a set number of hair follicles and the thickness of our hair is determined by the size of these follicles: thick hair grows out of large follicles, while fine hair grows out of small follicles. So, unfortunately, there is no product on earth that can make your hair thicker or increase the number of hair follicles on your head! A single hair might appear thin and fragile, but according to international cosmetics giant L’Oréal, tests have shown that a healthy hair can carry a weight of about 100g (0.2 lb). If you multiply this by 120 000 – the average number of hairs on the human head – you can deduce that a head of hair could, theoretically, support 12 tonnes (in reality, of course, the scalp is not strong enough to make this possible).

      The growth factor

      Just like there are changes to the body and skin, your hair’s structure and its appearance also change as you grow older.

      ■ Babies are born with a specific, genetically determined number of hair follicles. Yet some babies have hardly any hair at birth, while others have quite a bit. This is no indication of what the state of their hair will be later in life!

      ■ Small children’s hair often has characteristics that are lost later in life. For example, blonde hair may darken as they grow older and curls may disappear. The thickness of children’s hair increases fast until the age of three or four. The diameter continues to increase more slowly until the age of 10 or 11, when the hair should be at its thickest.

      ■ In puberty, the body undergoes a number of metabolic changes. These also affect the hair. The sebaceous glands are stimulated, often secreting an excess of oil and resulting in oily hair. Dandruff can also appear at this stage, the result of oil secretion and hormonal changes.

      ■ Around the age of 25, the diameter of hair starts to decrease. In the next 15 years the hair-growth cycle changes, with fewer hairs in the anagen phase and more in the resting phase. Hair growth thus slows down.

      ■ The age at which grey hairs start appearing is genetically determined. Hair turns white when melanin is no longer produced. Individual hairs become thinner. Many men start losing their hair, and a percentage of women experiences some thinning.

       This baby’s sparse hair is no indication of what her hair might look like in future, and her sister may still find her blonde hair darkening.

      Defining your ethnic hair type

      Human hair – which grows everywhere on the body except the palms of the hands, soles of the feet, eyelids and lips – can differ markedly in texture and colour. Yet all human hair has similar functions. Scalp and body hair is believed to keep us warm by preserving heat. It cushions our heads, giving some protection against injury. The hair inside our nose and ears and around our eyes protects against dust and germs, while eyebrows and eyelashes protect our eyes against sweat, harsh light and tiny particles. Armpit hair helps to reduce friction.

      Unlike other mammals, humans do not moult, because our hair follicles are all at different stages of the growth cycle at any given time. (If they had all been synchronized, everybody would have gone bald from time to time.) Nevertheless, we do shed our hair at a rate of 50 to 80 scalp hairs a day (the figure of 100 hairs a day, often quoted as the average daily hair loss, is now believed to be exaggerated). As we’ll see later, factors like changing hormone levels, diet and medication can influence the hair-loss rate quite drastically.

       Your hair type is determined by your genetic make-up; you can change your look, but not your hair’s inherent characteristics.

      In a class of its own

      Human hair can be coarse and black, fair and fine, straight and thick, wavy or kinky, but despite the different variations in colour and texture, it is generally classified into three ethnic types: Caucasian, Asian and African.

      Although the hair of most Scandinavians differs markedly from that of a South American or Spaniard, they all have hair that can be classified as Caucasian. The same goes for Indonesian and Japanese hair – both are Asian hair types. Typical Caribbean hair is classified as African hair. Even though there are variations within hair types, the three main ethnic classifications have very distinctive characteristics.

      Your hair type is determined by your genetic make-up and although there are ways to temporarily change its look, you can never change its inherent characteristics.

       CHANGING YOUR LOOK

      Unlike facial features or body shape, hair is relatively easy to change, and the hair products industry is booming, with industry players spending millions on research each year. A crucial element to offering consumers what they want and need is a thorough understanding of hair types.

      The chemical compositions of the three ethnic hair types, and the molecular structure of the keratin therein, are all similar, but the hair shafts differ. While there is some understanding of the reasons for this, research into the differences continues.

      African hair is dark and tightly curled; Asian hair tends to be straight, coarse, dark and thick, while Caucasian hair ranges from fine and straight to relatively thick and wavy, and has the greatest variation in colour. The differences between the hair types, according to international hair products company Wella, centre on its longitudinal and cross-sectional shape, thickness, ellipticity (whether the hair is ‘round’ or ‘flat’) and colour.

      HOW HAIR TYPES DIFFER IN SHAPE

       Asian hair: This hair type has an approximately round shape.

       Caucasian: This hair type has an oval shape.

       African: This hair type is extremely oval, almost flat.

       An example of typical Caucasian, African and Asian hair types. Caucasian hair has the greatest variation in texture and colour.

      Texture

      A strand of Caucasian hair has an average thickness of 0.07mm (3in) and, seen in cross section, has an oval shape. Coarser Asian hair, about 0.09mm (3.5in) thick, has an approximately round shape, while African hair, ranging between 0.04 (1.6in) and 0.12mm (5in) in thickness, is ex- tremely oval (nearly ‘flat’).

      It is generally no longer believed that the shape of a curly hair is caused by a curved hair follicle. The follicles of curly hair are, in fact, straight. Further evidence that follicle shape has nothing to do with the curliness