Armpit hair typically starts growing during puberty as a result of rising hormone levels. The growth of armpit hair signals that a child has started puberty and is developing secondary sex characteristics. While the timing varies for each child, armpit hair often begins between ages 9-15 for girls and ages 10-16 for boys.
Overview of Puberty Stages
Puberty is the process of physical changes through which a child’s body matures into an adult body capable of sexual reproduction. Puberty typically occurs between ages 8-14 for girls and ages 9-15 for boys. Puberty happens over a period of several years and includes major changes in height, weight, body composition, and reproductive development.
Puberty can be divided into the following stages:
- Prepubescent: No signs of puberty have started yet. The body resembles a child’s.
- Adrenarche: Hormones start rising. Pubic and underarm hair begin growing. This stage can start as early as age 6-8.
- Gonadarche: Sex organs and gonads start developing. Ovaries and testes increase hormone production.
- Full puberty onset: Rapid growth, development of breasts and genitals, menstruation and spermarche begin.
- Completion: Adult sexual characteristics have fully developed and pubertal growth stops.
Tanner Stages
Puberty is also commonly classified into the five Tanner stages, which track physical development:
- Stage 1: Prepubescent
- Stage 2: Breast and testicular enlargement, pubic hair growth
- Stage 3: Further enlargement and darkening of genitals and areola, more pubic hair
- Stage 4: Penis, scrotum and breasts reach nearly adult size, full pubic hair
- Stage 5: Adult genitalia and pubic hair pattern
When Does Armpit Hair Start Growing?
The growth of armpit hair signals the beginning of adrenarche, which represents the early stages of puberty. Here is when armpit hair typically first appears:
- Girls: Age 9-15, average age 11
- Boys: Age 10-16, average age 12
For both genders, underarm hair usually begins growing about one year after pubic hair appears. The whole process is influenced by genetics, race, body fat percentage, and general health.
Girls
In girls, the first appearance of armpit hair correlates with Tanner stage 2 of puberty. At this stage:
- Small breast buds form, with the areola widening
- Sparse pubic hair begins growing
- The first underarm hairs appear
- A growth spurt may begin
- Vaginal discharge increases
Menstruation typically begins about 2 years after breast and pubic hair growth start. So for most girls, getting their period happens sometime after underarm hair appears.
Boys
In boys, underarm hair growth marks the beginning of Tanner stage 3 of puberty. At Tanner stage 3:
- The penis and testes continue growing
- Pubic hair gets thicker and coarser
- Underarm hair grows
- Facial hair starts developing
- The voice starts deepening
For boys, the first ejaculation of semen (spermarche) typically happens about one year after getting underarm hair.
Other Signs of Early Puberty
In addition to armpit hair growth, other physical developments occur around the same time in early puberty:
- Growth spurt
- Oily skin and acne
- Body odor
- Pubic hair
- In girls, breast development and widening hips
- In boys, testicular and penile enlargement
These changes are all normal parts of growing into an adult. However, if signs appear at age 8 or younger in girls and 9 or younger in boys, it is considered precocious puberty and should be evaluated by a doctor.
Role of Hormones
Puberty is controlled by hormones produced in the body. The main hormones involved are:
- Estrogen: Peaks in females to stimulate breast growth, menstruation, pubic/underarm hair, and other feminine traits.
- Testosterone: Rises in males to stimulate muscle growth, voice deepening, facial hair, and other masculine traits.
- Growth hormone: Increases in both genders, spurring the adolescent growth spurt.
The activation of the hormonal system that controls puberty is not well understood, but likely involves signals from the brain and gonads. Genetics and environmental factors also influence timing.
Testosterone and Androgens
In both boys and girls, androgens (male sex hormones) start rising at the beginning of puberty. The main androgen is testosterone. Even though females have lower testosterone, the androgen surge they experience causes pubic and underarm hair to start growing.
Ethnic and Genetic Differences
Genetics can significantly influence the timing and progression of puberty. Some key differences between ethnicities include:
- On average, black girls start puberty the earliest, followed by non-Hispanic white girls, then Hispanic girls.
- Asian girls on average start puberty last.
- Black boys tend to start puberty earlier than boys of other ethnicities.
- Mexican-American boys start puberty slightly earlier than non-Hispanic whites.
However, there is considerable overlap between ethnicities. Individual variation based on genetics, nutrition, body weight, and environmental factors also affect pubertal timing.
Environmental Factors
Aside from genetics, other factors can influence when a child starts puberty:
- Body fat: Girls with higher body fat often begin puberty at younger ages.
- Physical activity: High activity levels may delay puberty slightly.
- Nutrition: Poor childhood nutrition can delay puberty.
- Stress: Chronic psychological stress may accelerate puberty.
- Chemicals: Endocrine disruptors and toxins in foods can impact hormones.
Exposure to chemicals from household products, plastics, and pesticides have been most closely linked to early puberty, especially in girls. Maintaining a healthy body weight through diet and exercise helps ensure normal timing.
When to See a Doctor
Consult a pediatrician if armpit hair or other puberty signs occur at any of these ages:
- Girls under age 8
- Boys under age 9
- Girls who haven’t started puberty by age 13
- Boys who haven’t started puberty by age 14
Seeking medical evaluation is important if early or delayed puberty occurs to rule out any underlying health conditions. Early puberty can be treated with medication if needed.
Managing New Armpit Hair
For both girls and boys, growing underarm hair for the first time can feel embarrassing and uncomfortable. Here are some tips for managing new armpit hair growth:
- Use an electric trimmer or scissors to trim hair short if desired.
- Ask a parent about trying over-the-counter hair removal creams.
- Wash regularly with soap and water to control odor.
- Use an antiperspirant deodorant to reduce wetness and bacteria.
- Avoid irritating skin with razors until older.
- Remember that armpit hair growth is normal and natural.
The Later Stages of Puberty
Armpit hair marks just the beginning of puberty. Further changes lie ahead:
- More hair growth on legs, arms, face, chest, and pubic area.
- Acne outbreaks.
- Body odor.
- Continued breast development in girls.
- Facial hair and voice deepening in boys.
- Rapid weight and height changes.
- Sexual maturity and fertility.
- Menstruation and sperm production.
The process takes several years. Staying informed about what lies ahead and maintaining open communication with parents can help young teens transition smoothly through this transformational time.
Conclusion
Armpit hair growth marks entry into puberty for both girls and boys. The first appearance of light, soft underarm hair typically happens between ages 9-15 in girls and 10-16 in boys. Armpit hair starts growing due to rising androgen hormones in early puberty. Seeing underarm hair is a sign that a child’s body is beginning to mature sexually and take on adult characteristics. While growing armpit hair can feel embarrassing or awkward at first, it simply reflects a normal part of development that everyone goes through. With support from parents and understanding of the changes ahead, teens can move through puberty with confidence.
