The breasts can enlarge if you are overweight, simply because fat has settled there. They can also enlarge because the actual breast tissue is overdeveloped; this is called gynaecomastia.
Usually both breasts are equally affected, but sometimes development of one is more obvious than the other.

If one breast is more enlarged than the other, ask your doctor to check it; breast cancer is rare in men (about 1% of all breast cancer is found in the male breast), but it can occur.

How Breasts Develop

Even a newborn baby has some basic breast tissue, which started to develop when it was a 6-week-old foetus. Before puberty, the breasts are the same in girls and boys. They consist of tiny branching tubes embedded in packing tissue. The glands for making milk have not yet formed.

At puberty, hormone levels start to rise. In females, the main hormone is oestrogen (the ‘female hormone’). Oestrogen makes the tubes thicken, lengthen and become more branched, and also stimulates the development of glandular lobules.

In men, the main sexual hormone is testosterone. This is made mainly in the testicles. The level of testosterone rises at puberty to 30 times the level it was previously. Men normally also have a small amount of oestrogen; at puberty, it rises to only three times the level it was before. This often makes the breast tissue grow slightly in teenage boys (see below), but eventually the high levels of testosterone take over completely and prevent the oestrogen having any further effect on the breast. Therefore, glandular lobules do not form in men. Instead, the breasts flatten out, and remain as a collection of tubes in packing tissue, just as they were before puberty.

Breast Growth in Teenage Boys

Teenage boys sometimes notice that their breasts are enlarging and/or are tender. This is nothing to worry about and happens to about half of all boys at some time. It does not mean you are changing sex! It can start any time after the age of about 10, and the breasts may be quite large by the age of 13 or 14. In the mid-to-late teens, they start to become smaller again, and will usually have flattened out by age 18 or 19.

Results of some surveys of breast enlargement in normal teenage boys

Normal teenage boys examinedThose with breast enlargement
1,865 American scouts, aged 10–160.39
993 Turkish schoolboys, aged 9–170.07
29 American schoolboys, at puberty0.69
681 Italian schoolboys, aged 11–140.33
135 Swiss youths, aged 8.5–17.50.22
377 American schoolboys, aged 10–150.49

Source: New England Journal of Medicine 1993;328:490–495


Why it happens. At puberty, the testosterone level does not rise steadily. Over the first few teenage years, it continually fluctuates wildly and, on some days, the level will dip quite low. These dips in testosterone allow the small amount of oestrogen that circulates in the blood of all men, to have an effect on the breast. This stimulates the growth of the packing tissue and tubes, so that the breasts enlarge. In men over about 15 years of age, the testosterone settles at a more steady, high level. This prevents the oestrogen from having an effect any longer, and the breast tissue usually starts to shrink.

What if the breasts remain enlarged? In only a few men, the breasts remain enlarged at the end of the teen years. This is not usually because there is anything wrong with the male hormones, but because the enlarged breast tissue has remained hypersensitive to the tiny normal amounts of oestrogen, or else is not responsive to the ‘shutting down’ effect of testosterone. Occasionally, a rare medical condition may be responsible, so consult your doctor to check your hormone levels. If everything is normal (which it usually is) a surgeon can remove the excess breast tissue.

Breast Enlargement in Men

It seems that breast tissue is very sensitive to the balance between oestrogen and testosterone in the blood. If there is either a fall in the testosterone level or a rise in the oestrogen level, the breasts will be stimulated to grow.

Obesity is a common cause. If you are overweight, the breasts will of course be larger because they are more fatty. In addition, fat produces oestrogen which stimulates breast development.

Medications are the other most likely reason. Some drugs have an oestrogen-like effect on the breast, and some block the effect of testosterone. Oestrogens are easily absorbed through the skin; men have developed breasts after using anti-balding scalp creams containing oestrogen, and even by absorption through the skin of the penis from a partner using a vaginal oestrogen cream.

Drugs that can cause breast enlargement in men

  • Oestrogen
  • Body-building steroids

Psychiatric drugs

  • Phenothiazines (such as chlorpromazine)
  • Tricyclic antidepressants (such as amitriptyline)
  • Benzodiazepines (such as diazepam)
  • Opiates

Drugs for hypertension or heart problems

  • Calcium-channel blockers (such as nifedipine, verapamil)
  • ACE inhibitors (such as captopril, enalapril)
  • Digoxin
  • Amiodarone
  • Spironolactone
  • Methyldopa

Drug misuse

  • Alcohol
  • Marijuana
  • Heroin, methadone
  • Amphetamines

Drugs for duodenal ulcer

  • Omeprazole
  • Cimetidine
  • Ranitidine

Antibiotics and antifungal drugs

  • Isoniazid
  • Metronidazole
  • Ketoconazole

Alcohol abuse upsets both sides of the oestrogen–testosterone balance. It stimulates the liver to clear testosterone from the blood, so testosterone levels fall. It probably also reduces the ability of the liver to break down oestrogens, so levels rise. Fortunately, the liver can often recover if alcohol intake is reduced.

Tumours are a rare cause of breast enlargement. Breast cancer can occur in the male breast but is usually on one side only. Tumours in other parts of the body can sometimes produce hormones that make the breasts grow and may also cause erection problems and/or oozing of milk from the breast. If you have these symptoms, it is essential that you see your doctor straight away.

Breast Cancer

Breast cancer can occur in men. About 1% of all breast cancer is found in the male breast. Men usually present to their doctor later than women, when the cancer has ulcerated the skin, or when there is spread to the lymph nodes.
Breast cancer in men is just as treatable as breast cancer in women if it is found early enough. So if you have the slightest worry that you might have a lump in your breast, see your doctor straight away so that you can have tests and treatment if necessary. Other signs of breast cancer include a sore or rash on the nipple, discharge from the nipple, the nipple turning in, or a change in shape of the breast.

If you are a woman reading this, you may wish to educate the men in your life about male breast cancer.

Old age. It is natural for men’s breasts to enlarge in old age. This often seems to happen over a few months, after which no further enlargement occurs. The reason is partly that less testosterone is produced in old age. Also, in old age, the body often contains a higher proportion of fat, which produces oestrogens. In about 50% of people, the breasts will become smaller again in time.

What Your Doctor Can Do about Breast Enlargement in Men

See your doctor if you think your breasts are enlarging, even if you have worked out the most likely cause. Your doctor will be able to:

  • check whether the actual glandular breast tissue is overdeveloped, or whether the enlargement is simply fat
  • check your testicles (because they make most of the testosterone)
  • decide whether any drugs are likely to be responsible
  • do blood tests to measure various hormones, including testosterone.

The treatment will depend on the reason for the growth. It may simply be a matter of losing weight or cutting down your alcohol intake. If the problem is a low testosterone level, testosterone can be given by injection or as a patch. Tamoxifen – a drug that interferes with the action of oestrogen – is used by some specialists to reduce gynaecomastia. Another possibility is danazol, a drug that promotes the effect of testosterone. Danazol can have troublesome side effects, such as weight gain, acne, muscle cramps and nausea.
The excess breast tissue can also be removed by surgery.


First published on:
Reviewed and edited by: Dr Victoria Harmer
Last updated: October 2020

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