Terminal Hair: Puberty Growth Phases From Vellus Hair

Terminal hair is the body's thick, long, pigmented hair. The hair on your scalp is terminal hair, but it’s also found on other areas of the body.

Terminal hair is one of the two types of hair that children and adults have. The other, vellus hair, differs from terminal hair in several ways. During puberty, increased hormone levels cause velus hair to turn into terminal hair in certain areas.

A number of factors related to hormonal changes regulated by the endocrine system affect the development of terminal hair and influence when and how it grows. 

Vellus vs. Terminal Hair

Aside from the palms of the hands, the soles of the feet, and the mucous tissues, the entire human body is covered with hair. Not all body hair is the same, though.

Vellus hair is the thin, short, soft, peach-fuzz-like hair that covers most of the human body. It replaces lanugo, an even softer, thinner type of hair found on babies in utero. Lanugo may also be present for the first few weeks after birth.

Vellus hair is thought to primarily serve as insulation for the body.

Terminal hair is known as mature hair. It’s thicker and grows longer than vellus hair.

During puberty, hormones will change some vellus hair follicles into terminal hair follicles. Teens develop thicker hair in certain areas, such as under the arms and around the genitalia, as a result.

Purpose of Terminal Hair

Terminal hair has several different purposes. For instance:

• Eyelashes and nose hairs provide a barrier to dust and dirt.
• Hair on your scalp may regulate the temperature of the head.
• Pubic hair blocks bacteria from entering the body and may protect you from sexually transmitted diseases.
  

Growth Phases

The development of terminal hair is considered one of the secondary sex characteristics, like breast and penis growth, that occurs during puberty.

Androgens, a group of sex hormones released during puberty, trigger these changes. Different parts of the body are especially sensitive to these hormones.

Male and Female Puberty Hair Growth

Puberty typically begins in boys between the ages of 9 and 15 and in girls between ages 8 and 14. During these years, both boys and girls grow terminal hair under the arms and in the pubic areas. In fact, in the early stages of puberty, terminal hair growth is concentrated in the pubic area.

However, there are significant differences in how and where hair appears for males and females in the pre-teen and teen years.

Girls during puberty:

• Keep more of their vellus hair compared to boys
• Grow thick leg hair
• Develop terminal hair in the pubic area
• See terminal hair in armpits

Boys during puberty:

• Experience terminal hair in more parts of the body than girls
• Develop thick hair in the pubic area (usually starting at the base of the penis)
• See terminal hair in armpits
• Grow thicker hair on the face, chest, back, legs, arms, hands, and feet
• Have some facial hair appear in their early teens, which may not fill in until their early 20s
  

Delayed or Missed 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.

Several disorders can also cause delayed puberty which will affect hair growth. These conditions include:

• Diabetes
• Kidney disease
• Cystic fibrosis
• Malnutrition
• Eating disorders
• Abnormalities in the thyroid and pituitary gland
• Asthma

In some cases, terminal hair doesn't grow at all. Genetics are most often to blame for these incidents.

Excess Growth

Approximately 7% of women experience a condition known as hirsutism. Related to an excess of androgens among other factors, hirsutism refers to hair growth in women that appears more like that in men.

Women with hirsutism may develop facial hairs (such as a mustache) and increased hair in their armpits and genital region.

Premature 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 things such as topical ointments.

Aging and Balding

Just as terminal hair growth is affected by hormones, terminal hair loss is often also the result of hormonal changes. Specifically, hormonal changes that are more prevalent as you age will affect hair growth on the head.

Most of the body is not affected by these hormonal changes. For instance, adults are unlikely to experience terminal hair growth changes in the pubic region, under the arms, and, for men, on the face.

Androgenetic Alopecia

Known commonly as male-pattern baldness (or female-pattern baldness), androgenetic alopecia is the most common form of hair loss in men and women. Researchers believe there is a genetic component that results in a change in how androgens affect the hair follicle.

Androgenetic alopecia can occur at any time after puberty, but the risk increases with age, and it is most common among white males. About 50% of white men over 50 have androgenetic alopecia. It is less common in women, but among women over 70, 38% have the condition.

Two treatments are currently approved for androgenetic alopecia:

• Minoxidil: This is available as an oral and topical medication. The oral is taken daily. The topical formula is applied directly to the scalp of men and women experiencing androgenetic alopecia. It's most effective at stopping the progression of hair loss, but it also stimulates the growth of new hair. Minoxidil can cause hair regrowth in six to 12 months, but you should continue using it ongoing since hair loss will occur if you stop using it.
  
• Finasteride: This is an oral medication taken daily. It's approved to treat androgenetic alopecia in men when minoxidil does not work; it is often used with minoxidil. It too is most effective at stopping hair loss.

Summary

Soft, fine hair that covers your body from infancy is known as vellus hairs. Thicker, coarser hair is known as terminal hair. Due to hormonal changes during puberty, some vellus hair follicles will become terminal hair follicles, resulting in thick hair in certain areas of the body. Both boys and girls develop terminal hair in the pubic area and under the arms. Boys will also develop facial hair and thicker hair on other areas of the body.

Certain genetic factors and medical conditions can result in terminal hair developing earlier or later than usual. They may also result in women developing too much hair or hair on the face or other parts of the body.

As adults age, hormonal changes once again affect the growth of terminal hair. This can result in male-pattern baldness, which affects females as well as males. Medication can help reduce the amount of hair you lose from this condition.

A Word From Verywell

Hair growth around the genitalia is one of the first signs of puberty. Parents may be surprised to see this indication of adolescence occurring in a pre-teen, but it's a natural change. As this and other signs of maturity take place, it's important to explain to children that they are normal and part of a healthy, growing body.

If terminal hair doesn't appear until the teen years, don't worry. This too can be normal, especially if other family members hit puberty a little late. However, be sure to talk to your pediatrician about any signs of delayed growth.

As adults age, concerns about terminal hair loss may affect self-esteem or self-image. There are effective ways to manage hair loss, though, including medication as well as diet and new approaches to hair styles and personal fashion.