The causes of gynecomastia: hormones, medicines, illnesses, lifestyle

Understanding why your chest has changed often means finding part of the solution. If the cause is a medicine that can be swapped, a product you can stop or a hormonal imbalance that can be corrected, recent gynecomastia can shrink without any other treatment. Here are all the known causes, from the most common to the rarest.

One shared mechanism: the hormone balance

Every cause of gynecomastia works through the same mechanism. The male breast gland is stimulated by oestrogens and held back by androgens, including testosterone. It grows as soon as the balance tips:

• either because oestrogens rise (more production, more conversion of testosterone into oestrogen, slower clearance by the liver);
• or because androgens fall (less active testicles, a hormone that blocks their action);
• or because the gland becomes more sensitive to oestrogens, or less sensitive to androgens.

How the causes break down

In adults who see a doctor about gynecomastia, the classic breakdown, from the reference review in the New England Journal of Medicine, is as follows:

Above all, remember this: in half of cases, there is no illness behind it. It is either gynecomastia with no cause found, or teenage gynecomastia that never fully went away.

1. Physiological causes

These are the most common, and they are not a sign of any illness.

• At birth: the mother’s hormones cross the placenta. Most newborns have a small breast bud that disappears within a few weeks.
• At puberty: for a few months, oestrogen production rises faster than testosterone. Nearly one boy in two develops gynecomastia, which usually goes away within 6 months to 2 years. See gynecomastia in teenagers.
• With age: testosterone gradually falls and body fat increases. Fat contains aromatase, the enzyme that converts testosterone into oestrogen. More than half of men over 50 have gynecomastia on examination.

2. Medicines and other substances

This is the most important cause to identify, because it is often reversible. Medicines account for 10 to 25% of gynecomastia in adults. The main families involved:

This list is not exhaustive. A French pharmacovigilance study based on reported side effects confirmed the weight of several of these families, especially anti-androgens and spironolactone.

Everyday substances

• Anabolic steroids, prohormones and some muscle-building products are a very common cause in young athletes. They have their own article: gynecomastia, bodybuilding and steroids.
• Cannabis is often mentioned. Cases have been described, but studies have not formally established the link.
• Alcohol acts mainly through liver damage and calories.
• Lavender and tea tree essential oils, applied repeatedly to the skin, have been linked to gynecomastia in young boys, reversible once stopped. These oils have a weak oestrogenic and a demonstrated anti-androgenic effect in the laboratory.
• Skin contact with a hormone gel (testosterone or oestrogen) used by someone close can be enough to have an effect.

3. Illnesses

These are less common, but they are what the examination and tests are looking for.

Liver disease

Cirrhosis, whatever its cause (alcohol, hepatitis, fatty liver), is a classic cause. A damaged liver clears hormones less well, and more testosterone is converted into oestrogen. Malnutrition followed by rapid refeeding (“refeeding gynecomastia”) works in a similar way.

Testicular problems (hypogonadism)

When the testicles produce too little testosterone, the balance tips. The causes vary:

• Klinefelter syndrome (an extra X chromosome), often diagnosed late, which combines small firm testicles, gynecomastia and sometimes infertility;
• the after-effects of mumps or testicular injury;
• secondary hypogonadism, when the pituitary gland no longer stimulates the testicles enough.

Hormone-producing tumours

This is why the doctor always examines the testicles. Some testicular tumours produce oestrogen or hCG, which stimulates the breast gland. They are rare (around 3% of cases) but very treatable when caught early. Even more rarely, a tumour of the adrenal gland or lung may be responsible.

Other illnesses

• Hyperthyroidism (an overactive thyroid) increases oestrogen.
• Kidney failure, especially in patients on dialysis.
• Excess prolactin, a hormone made by the pituitary gland, often caused by medicines.
• Obesity, which combines chest fat with increased oestrogen production by fat tissue.

The tests: how the doctor finds the cause

The work-up is guided by the examination:

1. Questions cover every medicine, supplement and sports product, alcohol, cannabis, how long it has been there and how it has changed.
2. The examination covers the breasts, testicles, thyroid and signs of liver disease.
3. Blood tests, depending on the context, include total testosterone, oestradiol, LH, FSH, prolactin, hCG, TSH, and liver and kidney function.
4. Imaging: breast ultrasound if in doubt; testicular ultrasound if the examination or blood tests point that way.

Interpreting the results follows a simple logic. A raised hCG means looking for a tumour. Low testosterone with high LH suggests a testicular problem. Low testosterone with low LH points to the pituitary. A high oestradiol means looking for a source of oestrogen.

In a teenager with a normal examination, and in an adult whose gynecomastia is old, stable and has no unusual features, the work-up is often minimal.

And if no cause is found?

That is common and rather reassuring: it means no illness has been identified. “Idiopathic” gynecomastia is managed like any other:

• if it is recent, medical treatment can be discussed (treatment without surgery);
• if it is long-standing and bothersome, surgery is the permanent solution (surgery);
• in every case, a compression garment hides it day to day.

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