Average Growth Rate for Hair

Not everyone can grow long locks.

Hair growth is a universally fascinating subject. Across almost every culture, inordinate attention is given to the hair on the head, and social significance is attached to hair style. Very long hair is especially interesting, not only because it takes years to achieve lengthy locks, but because not everyone can do it. Despite all the shampoos and other preparations we put on our heads, hair growth is ultimately limited by biological factors.

Features

Each hair on the body has its own growth cycle consisting of three phases. Anagen is the period during which the cells are deposited on the hair shaft in the hair follicle, lengthening the hair. During catagen, the hair stops growing and the follicle retracts. During telogen, the follicle rests. The hair may be shed during the telogen phase or it may be pushed out of the follicle by a new hair as anagen begins again.

Time Frame

The length of each hair growth phase varies widely among individuals. It also varies depending on the type of hair and its location on the body. For hairs on the head, a normal anagen phase can last anywhere from two to six years, catagen lasts one to two weeks, and telogen lasts five to six weeks. An average head hair grows about 6 inches a year during its anagen phase.

Function

The duration of anagen limits the maximum length of the hair. At any given time, approximately 85 percent of the hairs on a person's head are in the anagen phase. The rate at which the hair grows is also a determining factor in hair length. On average, waist-length hair requires an anagen phase of about six years.

Effects

Health conditions and medical treatments can have a dramatic effect on hair growth. Malnutrition can cause a percentage of hair follicles to stop growing hair, and the remaining follicles to produce fine, fragile hair. Chemotherapy often causes the complete cessation of hair growth. In both these cases, hair regrows when diet improves or after chemotherapy concludes. Other conditions such as alopecia areata can cause complete baldness that is sometimes irreversible. The causes of alopecia are not yet fully understood.

Considerations

Some people have an anagen phase that is longer than the norm. These people may be able to grow floor-length or longer hair. Conversely, an abnormally short anagen phase accounts for the difficulty some people have growing hair even to shoulder length. Hair breakage due to chemical or heat processing or inherent fragility may also significantly affect hair length, but is not related to hair growth.

Misconceptions

Male pattern baldness is caused by normal male hormones and genetic predisposition, and is not related to hair or scalp health. Therefore, remedies that claim to reduce or reverse hair loss by moisturizing or delivering vitamins to the scalp are ineffective. Hair creams that counteract male hormones locally at the scalp have been shown to reduce hair loss in some men, however.

Resources

• American Hair Loss Association