Signs of Puberty: What Happens to Your Body?

Puberty refers to the time when a child’s body goes through physical and emotional changes to become sexually mature. Changing hormone levels trigger the start of puberty and cause several physical changes.

Children assigned male at birth experience a growing penis, body hair, and a deepening voice. Children assigned female at birth experience growing breasts, widening hips, and periods (menstruation). 

Puberty's meaning often needs to be understood or clarified. The average age to start puberty is between 10 and 14 for girls and 12 and 16 for boys. However, it is common for children, tweens, and adolescents to experience puberty before (early) or after (delayed) these average timeframes.

Hormone Changes in Girls vs. Boys

Puberty begins when a child’s hormones begin to change. In a boy, the hormones trigger the testicles to make testosterone and sperm. In a girl, hormones trigger the ovaries to make estrogen and produce and release eggs. Children of all sexes can expect to experience skin changes such as acne and a growth spurt. 

In Girls

During puberty, children with ovaries experience an increase in estrogen levels, and this can lead to several physical changes including: 

• Breast buds (small, firm, tender lumps under the nipples)
• Breast development
• Dark, coarse, curly hair around the labia 
• Pubic hair
• Underarm hair 
• Widening hips
• Gains in body weight and body fat 
• The first menstrual period (usually begins two years after breast buds appear)

Most girls experience a growth spurt about one to two years before their periods start. After the period starts, they can expect to grow another 1 to 2 inches in total.

In Boys

Children with testes experience an increase in testosterone levels during puberty, and this can lead to the following physical changes: 

• Growing penis and testes
• Dark, coarse, curly hair above the penis and on the scrotum
• Erections happen more often
• Ejaculation happens 
• Underarm hair
• Facial hair 
• Voice changes and deepening 
• Shoulders broaden
• Weight and muscle gain 

Most boys experience a growth spurt between the ages of 12 to 15. By age 16, a boy’s height will likely not change. However, the person can still gain muscle mass. 

Average Age When It Starts 

The average age to start puberty is between 8 and 13 for girls and 9 and 14 for boys. However, these time frames depend on various factors. 

Puberty starts when an area in the brain called the hypothalamus signals to the body that it is time to begin developing the external reproductive organs, as well as the breasts, skin, muscles, bones, hair, and brain. 

Early Puberty

Early puberty occurs when a child begins to experience the physical changes of puberty at a younger age. Girls who start puberty before age 8 and boys who begin puberty before age 9 are considered to have early (precocious puberty). Most children who experience early puberty have a family history of parents going through early puberty as well. 

The two types of early puberty include:

• Central precocious puberty (CPP) occurs when the hypothalamus activates puberty early. There is usually no underlying medical problem.
• Peripheral precocious puberty (PPP) is rarer than CPP and results from the early production of sex hormones caused by problems with the ovaries, testicles, or adrenal glands.
  

Contributing Factors

Researchers are not certain why some children go through early puberty. Children with central precocious puberty (CPP) do not have a physical health problem that causes early hormonal changes, and the cause is usually unknown. 

Early puberty is more common in girls than boys. Possible causes or risk factors may include:

• Family history of early puberty
• Central nervous system disorders
• Tumor in the brain, ovaries, or testes 
• Brain trauma or inflammation 
• Hypothyroidism (underactive thyroid)
• Genetic syndromes 

Delayed Puberty 

Boys who begin puberty after age 14 and girls who begin puberty after age 13 are considered to have delayed puberty. Many adolescents with delayed puberty have a family history of parents with delayed puberty. 

"Constitutional delayed puberty" is the term for late puberty in healthy adolescents when the cause is unknown. This is the most common type of delayed puberty. 

Boys may be diagnosed with delayed puberty if their penis and testicles do not start to grow by age 14. The child may also be shorter than many of their peers. 

Girls may be diagnosed with delayed puberty if their breasts have not begun to develop by age 13. The first sign of puberty in most girls is the development of breast buds. 

Contributing Factors

Delayed puberty in adolescents has several possible causes. Isolated gonadotropin deficiency (IGD) is a chronic condition that causes deficiencies in the hormones that start puberty: luteinizing hormone (LH) and follicle-stimulating hormone (FSH). This condition is present at birth and is usually diagnosed in infancy or childhood.

Chronic conditions that may cause late development in boys include:

• Inflammatory bowel disease (IBD): A group of disorders, including Crohn's disease and ulcerative colitis) with inflammatory lesions in the digestive tract
• Sickle cell disease: A genetic condition that affects the red blood cells
• Cystic fibrosis: A genetic condition that affects mucus and sweat production, which impacts the digestive, respiratory, and reproductive systems

A common cause of delayed puberty in girls is a lack of body fat. Girls who participate in competitive gymnastics, dance, or swimming may not have enough body fat to trigger puberty. Girls with certain chronic illnesses or eating disorders may also experience severely low body fat levels. Eating more and gaining weight can help puberty begin. 

A less common cause of delayed puberty in girls is primary ovarian insufficiency. This occurs when the ovaries are damaged or do not develop properly. The most common cause of primary ovarian insufficiency is Turner's syndrome, a genetic disorder that occurs when all or part of one X chromosome is missing.

A Word From Verywell

If puberty starts too early or is delayed, it is very important to discuss it with your provider. Those issues have the potential to be abnormal, and there may be a need to determine the reason for the delay or early onset with various blood tests and/or bone-age X-rays.

— JONATHAN B. JASSEY, DO, MEDICAL EXPERT BOARD

How Do I Know If It's Happening?

Puberty involves several physical changes that tell you that your body is going through this process. If you are unsure if you have reached puberty, consider the following questions:

• Has my skin changed or become more oily lately?
• Do I feel like I have gotten taller? Have people commented on my increasing height?
• Do my emotions feel stronger or unpredictable? 
• Have I developed pubic hair or underarm hair?
• Does my body feel like it is changing?

Girls may consider the following questions:

• Have I noticed firm lumps under my nipples that feel tender?
• Do my breasts seem to be growing?
• Are my hips becoming wider?
• Am I gaining weight?
• Have I started getting periods every month?

Boys may consider the following questions:

• Have my penis and testicles started to grow?
• Am I noticing more erections?
• Am I having more ejaculations?
• Am I waking up with an erection, or already have ejaculated?
• Is my voice changing?
• Do my shoulders feel like they are getting broader?
• Have I gained weight?

Summary 

Puberty is a time when a child’s or adolescent’s body goes through several physical changes to become sexually mature. Hormonal changes trigger puberty and cause physical changes

In boys, an increase in testosterone leads to a larger penis and testes, a deepening voice, and muscle gain. In girls, an increase in estrogen leads to breast development, widening hips, and the start of menstrual periods.

The average age of puberty for girls is 8 to 13 and 9 to 14 for boys. Many people will go through puberty before or after these average timeframes.