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Different Types of Human HairLanugo hair is the first hair to be produced by the hair follicles of a developing foetus. It normally covers the foetus until the seventh or eighth month of gestation, is fine and soft and contains no medulla and no pigment. After it has been shed, it is replaced by vellus hair arid terminal hair. Newborn babies' bodies are covered with vellus hair, although they have terminal hair on their heads and eyebrows. The fine hair on parts of some adults' bodies is also vellus hair. These hairs are short, just a centimeter or two long, and they are soft, with no medulla. Occasionally, they contain pigment. Terminal hair, which grows on the head and also makes up beards, eyelashes and armpit hair, replaces vellus hair. These hairs are longer and coarser than vellus hair, often have a medulla and are usually pigmented. A touch of colourMelanin, found in the cortex, 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 water- proof and shiny. As all teenagers discover sooner or later, an excess of sebum leads to greasy hair. Too little of it causes dry hair. |
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