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What is gynaecomastia?

Gynaecomastia (sometimes referred to as "man boobs") is a common condition that causes boys' and men's breasts to swell and become larger than normal. It is most common in teenage boys and older men.

Signs of gynaecomastia

Signs vary from a small amount of extra tissue around the nipples to more prominent breasts. It can affect one or both breasts.

Sometimes, the breast tissue can be tender or painful, but this isn't always the case.

Causes of gynaecomastia

Hormone imbalance

Gynaecomastia can be caused by an imbalance between the sex hormones testosterone and oestrogen. Oestrogen causes breast tissue to grow. While all men produce some oestrogen, they usually have much higher levels of testosterone, which stops the oestrogen from causing breast tissue to grow.

If the balance of hormones in the body changes, this can cause a man's breasts to grow. Sometimes, the cause of this imbalance is unknown.


Being very overweight (obesity) is a common cause of gynaecomastia – this is because being overweight can increase levels of oestrogen, which can cause breast tissue to grow. If you're overweight you're also more likely to have excess fat that can enlarge the breast tissue. For some people losing weight or doing more exercise can help but this may not always improve the condition.

Newborn baby boys

Gynaecomastia can affect newborn baby boys, because oestrogen passes through the placenta from the mother to the baby. This is temporary and will disappear a few weeks after the baby is born.


During puberty, boys' hormone levels vary. If the level of testosterone drops, oestrogen can cause breast tissue to grow. Many teenage boys have some degree of breast enlargement. Gynaecomastia at puberty usually clears up as boys get older and their hormone levels become more stable.

Older age

As men get older, they produce less testosterone. Older men also tend to have more body fat, and this can cause more oestrogen to be produced. These changes in hormone levels can lead to excess breast tissue growth.

Other causes

Other rare causes of gynaecomastia include:

  • side effects of medicine – such as anti-ulcer drugs or medicine for heart disease
  • illegal drugs – such as cannabis or anabolic steroids
  • alcohol misuse
  • a health condition – such as kidney failure or liver disease
  • Klinefelter syndrome (a rare genetic disorder)
  • lumps or infection in the testicles

Treatment for gynaecomastia

See a GP if you're worried about breast tissue growth – they can discuss the treatment options with you.

Treatment options include

  • medication to adjust a hormone imbalance
  • surgery to remove the excess breast tissue

Male breast reduction surgery is not usually available on the NHS for the treatment of gynaecomastia.

The procedure is available at private hospitals and clinics.

Read more about male breast reduction surgery.

Always see a GP if the area is very painful or there's an obvious lump. Sometimes, the lump may need to be removed. Gynaecomastia isn't related to breast cancer, but you should see a GP if you're worried about breast swelling.

Read the answers to more questions about men's health.

Page last reviewed: 22 March 2021
Next review due: 22 March 2024