Hair growth has three alternating stages of growth: anagen, telogen and catagen. Anagen is the stage which lasts for years, and the stage where most of the hair growth occurs. Telogen is the transitional stage, in which the hair starts getting ready to be shed; this phase lasts for months. Catagen is the stage in which the hair is shed from the body, and this stage lasts for days. Hair growth depends on factors such as the inclusion of proper nutrients and vitamins in your diet, the amount of androgens being produced in the body and, very importantly, heredity.
History
According to The American Academy of Dermatology, hair follicles are created in the first trimester of pregnancy. It is during this period only that new hair follicles are formed; new hair follicles cannot be formed after birth. However, the color of the hair may change, factors can change the cyclic behavior, and the size of the hair may change throughout your lifetime. The head is the mostly densely populated area of hair follicles, and is home to the longest hair on the body.
Types
Vellus and terminal are the primary types of hair grown on the body. Vellus hair is found throughout the body; this hair is very soft, light and short. Terminal hair grows much longer and is coarse in texture. Terminal hair also contains melanin, which gives it a darker color. Melanocytes produce melanin, which is found at the base of the hair follicle, known as the bulb, according to Surviving Hair Loss.com. Most women have vellus hair in places where men have terminal hair, such as the back, face and chest.
Function
The purpose of vellus hair on your legs, arms, back and stomach is to regulate your body temperature and keep you warm in cold conditions. Terminal hair on the head is much longer and thicker in order to protect your scalp from being burnt by the sun. Eyebrows and eyelashes protect your eyes from sweat and small particles. Hair also provides your body with an external sensory unit; for example, movement of the hair alerts you to something crawling on your body. Additionally, when the hairs are touched, goose bumps can arise.
Puberty
With the onset of puberty, vellus hair becomes terminal hair in certain areas of the body. Both boys and girls begin producing terminal hair in the pubic region and under the armpits. This is due to an increase in androgen, a sex hormone grouped with testosterone. As boys mature, they will produce terminal hair on the face, chest, stomach and back. Depending on genetics, some individuals will start puberty earlier than others. Some children may be much hairier then others.
Considerations
When considering if your hair growth is normal or abnormal, there are certain factors to look for. Women may develop a condition known as hirsutism if their body begins to produce more androgen then estrogen. This imbalance of hormones causes an increase in terminal hair in places such as the face, chest and back. According to FamilyDoctor.org, a common condition that triggers hirsutism in women is polycystic ovary syndrome. Other factors that may cause abnormal hair growth can include menopause, the consumption of certain medications, and a more serious condition known as hypertrichosis. Hypertrichosis, a condition in which excessive amounts of hair are found all over the body, can be developed at birth or later in life from certain medical conditions, as well as other factors.
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