What Is Terminal Hair Growth During Puberty?

Adolescent students, an age when secondary sex characteristics such as terminal hair develop
What is terminal hair and how is it related to puberty and secondary sex characteristics?. Hero Images/Getty Images

What exactly is terminal hair, when does it appear as a secondary sex characteristic, and how does it differ from vellous hair?

What is Terminal Hair?

Terminal hair is the thick, long, pigmented hair found on the scalp, face, armpits and pubic area. The growth of terminal hair is influenced by hormones.

Origin of Terminal Hair

There are hair follicles all over the body. Within the follicles are stem cells, blood vessels, sebaceous glands and, of course, hair.

The follicle lies within the second layer of the skin: the dermis. This is the living part of the hair. The outer hair—that is, the hair you can see—is actually dead.

Vellus Hair

Aside from the palms of the hands, the soles of the feet and the mucous tissues, the entire human body is covered with vellus hair. Vellus hair, often called peach fuzz, is thin, short and light-colored. Unlike terminal hair, the growth of vellus hair is not influenced by hormones. Vellous hair is thought to primarily serve as insulation for the body.

Transformation of Vellous Hair into Terminal Hair Via Androgens

During puberty, increased hormone levels cause vellus hair to turn into terminal hair in certain parts of the body. Different parts of the body possess different levels of sensitivity to these hormones, known as androgens. The development of terminal hair is considered one of the secondary sex characteristics.

Androgens are known as male hormones because males produce and use androgens, like testosterone, more than females. Although these supposed "male" hormones are present in females—they play a lesser role—they are essential in male physical and sexual development.

Parts of the body that respond to these hormones include the pubic area and the armpits, which occurs in both males and females.

Females keep more of their vellus hair, while males develop terminal hair in more parts of the body, including, but not limited to the face, chest, back, legs, arms, hands, and feet.

Stages of Terminal Hair Growth

Puberty typically begins in boys between the ages of 9 and 15, and in girls between ages 8 and 14. In males, terminal hair appears throughout the teenage years, although where the hair appears changes.

In the early stages of puberty, terminal hair growth is concentrated in the pubic area (usually starting at the base of the penis) and armpits. Some facial hair appears early on, but it fills in during the final stages of puberty, typically by the early 20s. Females can expect to develop thicker leg hair and terminal hair in the pubic area and armpits during their teens.

Delayed Terminal Hair Growth

Terminal hair growth doesn't always occur as it should. The pituitary gland secretes hormones that initiate puberty, including luteinizing hormone, androgens, and progesterone in females. If these hormones aren't being secreted, puberty cannot occur. (Luteinizing hormone is made in the pituitary gland and stimulates the relates of estrogens from the ovary in women and testosterone from the testicles in men.)

Excess Terminal Hair Growth

Roughly 10 percent of women experience a condition known as hirsutism. Related to an excess of androgens among other factors, hirsutism refers to hair growth in women than appears more like that in men. Women suffering from hirsutism may develop facial hairs (such as a mustache) and increased hair in their armpits and genital region.

Early (Precocious) Terminal Hair Growth

In some cases, terminal hair begins to grow earlier than normal. The exact cause for premature puberty (precocious puberty) in males and females can't always be identified, but it's been linked to hormonal disorders and exposure to external hormones (estrogens and testosterone) through something like a topical ointment.

Absence of Terminal Hair Growth

In other cases, terminal hair doesn't grow. Genetics are most often to blame, but it's also caused by diabetes, kidney disease, asthma and abnormalities in the thyroid and pituitary gland.

Stimulation of Terminal Hair Growth

It's important for those who are on medications such as Minoxidil which can stimulate hair growth to know that these medications can stimulate the growth of terminal hair on the face, armpits, and groin as well. In other words, if the medication is resulting in more hair on your head you will probably need to shave more often as well.

Why are Some Terminal Hairs Short?

Unlike the terminal hair on top of your head, the growing phase of terminal hair related to secondary sex characteristics (anaphase), is shorter, in the range of months rather than the two to six years of head hair. For this reason the hair you have in your armpits or pubic region never gets long like the hair on your head.

Terminal Hair as We Age

Unlike the common male pattern baldness which is so prevalent, terminal hair which grows on the face, in the armpits, and in the pubic region usually continues to grow into old age. For this reason, a man may be completely bald on top of his bed but still be able to grow a beard.

Source:

Kasper, Dennis, Anthony Fauci, Stephen Hauser, Dan Longo, and J. Jameson. Harrison's Principles of Internal Medicine. New York: McGraw-Hill Education, 2015. Print.

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