What causes gynaecomastia?

Gynaecomastia can be due to the imbalance of the sex hormones, testosterone and oestrogen. Oestrogen is a female hormone that causes the breast tissue to grow. Men do produce some oestrogen but they usually have more testosterone which prevents the effects of oestrogen.

• Hormone imbalance in men can cause the breasts to grow.
• Obesity increases levels of oestrogen and is also a common cause for gynaecomastia.
• In newborn baby boys, oestrogen can pass through the placenta from the mother, but this is temporary and will disappear in a few weeks after birth.
• During puberty, hormone levels change and if the amount of testosterone drops, teenage boys can develop gynaecomastia. This usually clears up after their hormone levels stabilise and is uncommon beyond the age of 17 years.
• As men get older, they produce less testosterone and tend to have more fat and these can lead to excess breast tissue growth.
• Medications may sometimes cause gynaecomastia due to their side effects on the hormonal pathways.
  Common examples include:
  • Some heart medications such as spironolactone, verapamil, nifedipine, enalapril, digoxin and amiodarone
  • Antibiotics/antifungals like ketoconazole, isoniazid and metronidazole
  • Chemotherapy drugs like methotrexate and steroids
  • Psychiatric medications like haloperidol, diazepam and tricyclic antidepressants
  • Recreational drugs including alcohol, amphetamines and heroin
• Rarer conditions include tumours such as pituitary tumours in the brain, testicular tumours, lung, liver and kidney cancers, kidney, liver or thyroid disease or genetic causes such as Klinefelter syndrome.
• Sometimes the cause is unknown