As an adult, you probably remember puberty — a time when your body went through a lot of changes. And now you’re the parent of a child who’s experiencing these changes. You’ll want to know what to expect so you can help your child through each stage of development.

Professor James M. Tanner, a child development expert, was the first to identify the visible stages of puberty. Today, these stages are known as the Tanner stages or, more appropriately, sexual maturity ratings. They serve as a general guide to physical development, although each person has a different puberty timetable.

Read on to learn about the Tanner stages and what you can expect to see in boys and girls during each stage.

Tanner stage 1 describes a child’s appearance before any physical signs of puberty appear. Toward the end of stage 1, the brain is just starting to send signals to the body to prepare for changes.

The hypothalamus begins to release gonadotropin-releasing hormone (GnRH). GnRH travels to the pituitary gland, which is the small area under the brain that makes hormones that control other glands in the body.

The pituitary gland also makes two other hormones: luteinizing hormone (LH) and follicle-stimulating hormone (FSH).

These early signals typically start after a girl’s 8th birthday and after a boy’s 9th or 10th birthday. There aren’t any noticeable physical changes for boys or girls at this stage.

Stage 2 marks the beginning of physical development. Hormones begin to send signals throughout the body.

Girls

Puberty usually starts between ages 9 and 11. The first signs of breasts, called “buds,” start to form under the nipple. They may be itchy or tender, which is normal.

It’s common for breasts to be different sizes and grow at different rates. So, it’s normal if one bud appears larger than the other. The darker area around the nipple (areola) will also expand.

In addition, the uterus begins to get larger, and small amounts of pubic hair start growing on the lips of the vagina.

On average, African-American girls start puberty a year before Caucasian girls, and are ahead when it comes to breast development and having their first periods. Also, girls with higher body mass index experience an earlier onset of puberty.

Boys

In boys, puberty usually starts around age 11. The testicles and skin around the testicles (scrotum) begin to get bigger. Also, early stages of pubic hair forms on the base of the penis.

Physical changes are becoming more obvious.

Girls

Physical changes in girls usually start after age 12. These changes include:

  • Breast “buds” continue to grow and expand.
  • Pubic hair gets thicker and curlier.
  • Hair starts forming under the armpits.
  • The first signs of acne may appear on the face and back.
  • The highest growth rate for height begins (around 3.2 inches per year).
  • Hips and thighs start to build up fat.

Boys

Physical changes in boys usually start around age 13. These changes include:

  • Penis gets longer as testicles continue to grow bigger.
  • Some breast tissue may start to form under the nipples (this happens to some teenage boys during development and usually goes away within a couple of years).
  • Boys begin to have wet dreams (ejaculation at night).
  • As the voice begins to change, it may “crack,” going from high to lower pitches.
  • Muscles get larger.
  • Height growth increases to 2 to 3.2 inches per year.

Puberty is in full swing during stage 4. Both boys and girls are noticing many changes.

Girls

In girls, stage 4 usually starts around age 13. Changes include:

  • Breasts take on a fuller shape, passing the bud stage.
  • Many girls get their first period, typically between ages of 12 and 14, but it can happen earlier.
  • Height growth will slow down to about 2 to 3 inches per year.
  • Pubic hair gets thicker.

Boys

In boys, stage 4 usually starts around age 14. Changes include:

  • Testicles, penis, and scrotum continue to get bigger, and the scrotum will get darker in color.
  • Armpit hair starts to grow.
  • Deeper voice becomes permanent.
  • Acne may start to appear.

This final phase marks the end of your child’s physical maturation.

Girls

In girls, stage 5 usually happens around age 15. Changes include:

  • Breasts reach approximate adult size and shape, though breasts can continue to change through age 18.
  • Periods become regular after six months to two years.
  • Girls reach adult height one to two years after their first period.
  • Pubic hair fills out to reach the inner thighs.
  • Reproductive organs and genitals are fully developed.
  • Hips, thighs, and buttocks fill out in shape.

Boys

In boys, stage 5 usually starts around age 15. Changes include:

  • Penis, testicles, and scrotum will have reached adult size.
  • Pubic hair has filled in and spread to the inner thighs.
  • Facial hair will start coming in and some boys will need to begin shaving.
  • Growth in height will slow down, but muscles may still be growing.
  • By age 18 most boys have reached full growth.
Tanner stages in girlsAge at the startNoticeable changes
Stage 1After the 8th birthdayNone
Stage 2From age 9–11Breast “buds” start to form; pubic hair starts to form
Stage 3After age 12Acne first appears; armpit hair forms; height increases at its fastest rate
Stage 4Around age 13First period arrives
Stage 5Around age 15Reproductive organs and genitals are fully developed
Tanner stages in boysAge at the startNoticeable changes
Stage 1 After the 9th or 10th birthday None
Stage 2 Around age 11Pubic hair starts to form
Stage 3 Around age 13 Voice begins to change or “crack”; muscles get larger
Stage 4 Around age 14Acne may appear; armpit hair forms
Stage 5Around age 15Facial hair comes in

Acne can be a problem for both boys and girls. The changing hormones cause oils to build up on the skin and clog pores. Your child can develop acne on the face, back, or chest.

Some people have worse acne than others. If you have a family history of acne, there’s a higher possibility your child will also experience acne.

Generally, you can treat acne by washing the affected areas regularly with a mild soap. And there are also over-the-counter (OTC) creams and ointments to help control breakouts. You may want to try some home remedies as well.

For more severe acne, you may consider taking your child to see their pediatrician or a dermatologist. The doctor can recommend stronger prescription treatments.

Larger sweat glands also develop during puberty. To prevent body odor, talk to your child about deodorant options and make sure they shower regularly, especially after intense physical activity. Learn more about hygiene habits for kids and teens.

Puberty can be challenging for kids and parents. In addition to causing many physical changes, hormones are also causing emotional changes. You may notice your child is moody or behaving differently.

It’s important to react with patience and understanding. Your child may be feeling insecure about their changing body, including their acne.

Talk about these changes and reassure your child it’s a normal part of maturing. If something is particularly troubling, talk to your child’s doctor as well.