What causes gynecomastia? Hormones, medications, and steroids

Gynecomastia is caused by a shift in the balance between estrogen and testosterone activity in male breast tissue, and in practice that shift traces back to one of four things: a normal life stage, a medication, an underlying medical condition, or anabolic steroid use. Identifying which one applies is not academic. It determines whether a man's chest is likely to settle on its own, whether stopping a drug can reverse it, and whether surgery is the only route to a flat chest.

The mechanism is a ratio, not a single hormone. Every man produces small amounts of estrogen, and breast tissue responds to the relationship between estrogen and testosterone rather than to either hormone in isolation. When estrogen activity rises, testosterone activity falls, or the tissue becomes more sensitive to estrogen, the glandular tissue behind the nipple can proliferate. That is why gynecomastia shows up in situations as different as puberty, liver disease, and a steroid cycle: all of them tilt the same ratio. StatPearls, hosted by the NIH National Library of Medicine, reviews the etiology and workup of gynecomastia and notes that a large share of cases are ultimately classified as idiopathic, meaning no single cause is ever pinned down.

Normal life stages account for most cases. Three periods of life reliably produce hormonal gynecomastia. Newborn boys often have transient breast tissue from maternal estrogen, which resolves within weeks. Adolescents commonly develop it around ages 12 to 14 as puberty briefly raises estrogen ahead of testosterone, and the majority of these cases regress on their own within six months to two years. Older men develop it as testosterone declines with age and body fat, which converts testosterone into estrogen, tends to rise. A teenager whose chest has changed in the past year is often a candidate for watchful waiting rather than an operation, which is one reason a surgeon asks how long the tissue has been present before proposing anything.

Medications are the most overlooked cause. A long list of common prescriptions can trigger breast tissue growth, and men frequently arrive at a consultation without connecting the two. The StatPearls review groups the usual offenders into recognizable categories: anti-androgens and hormone-active drugs such as spironolactone, finasteride, and ketoconazole; the acid-reducer cimetidine; cardiac drugs including digoxin and some thiazides; certain psychiatric medications; and several chemotherapy agents. Alcohol and marijuana are also implicated. If the chest change began within months of starting a new drug, that timing is worth raising with the prescribing physician, because a medication-induced case caught early can sometimes improve after a supervised switch to an alternative.

Anabolic steroids are a leading cause in gym-focused men. Exogenous testosterone and many anabolic compounds are converted in the body to estradiol by the aromatase enzyme, and that surge in estrogen activity is precisely the signal breast tissue responds to. Men on cycles often notice tenderness or a firm button behind the nipple first, sometimes described as puffy nipples, before any visible change. Once glandular tissue has formed and matured, stopping the cycle does not reliably reverse it, and continuing to use anabolic agents after surgery is one of the few situations in which tissue can genuinely redevelop, which is covered in more depth in the discussion of whether gynecomastia comes back after surgery.

Medical conditions that move the hormonal balance. Liver disease and cirrhosis alter how the body clears estrogen, kidney failure and dialysis disturb hormone metabolism, thyroid overactivity raises circulating estrogen, and hypogonadism lowers testosterone directly. Rarely, tumors of the testis, adrenal gland, pituitary, or lung produce hormones that drive breast growth. These are uncommon relative to the everyday causes, but they are the reason a proper evaluation involves a physical exam and often blood work rather than a glance at the chest. Mayo Clinic covers the same range of causes and risk factors for gynecomastia, including the health conditions and drugs that most often sit behind it.

Some findings need evaluation before anything cosmetic. Male breast cancer is rare, but it can present as chest enlargement, so certain features warrant prompt medical assessment rather than a surgical consultation: rapid growth on one side only, a hard lump that feels fixed to the tissue beneath it, nipple discharge or bleeding, skin dimpling or retraction, or an enlarged lymph node in the armpit. MedlinePlus, the NIH patient library, describes when breast enlargement in males should be checked by a clinician and what tests may follow. Ruling this out first is standard practice and is not a sign that anything is wrong.

Fat and gland are different problems with different causes. Not every enlarged male chest is true gynecomastia. Pseudogynecomastia, also called lipomastia, is fat accumulation without glandular growth, and it tracks with body weight rather than hormones. True gynecomastia feels like a firm, sometimes tender, rubbery disk centered behind the areola, while fat is soft and spread more evenly across the chest. The distinction drives the operation: fat responds to liposuction, gland has to be excised directly, and mixed cases need both. That is the core of how surgeons approach gynecomastia and male breast reduction, and getting the assessment wrong is the most common source of an under-corrected chest.

Why the cause changes the plan. A case under a year old in a teenager is often observed. A case that began weeks after a new prescription may improve if the prescriber can substitute something else. A case caused by liver, kidney, or thyroid disease calls for treating the underlying condition first. But glandular tissue that has been present for roughly a year or longer tends to become fibrotic and scarred, and at that stage it rarely regresses with hormone management or weight loss. That is the point at which surgery becomes the realistic answer, and it is why long-standing cases are the ones most often treated operatively.

What to do before booking a procedure. The sensible order is medical first, cosmetic second. Start with a primary care physician or endocrinologist for a history, an exam, a full medication and supplement review, and any indicated hormone or liver and kidney testing. Bring the timeline: when the change started, whether it is tender, whether it is one-sided, and what medications or compounds were in use at the time. With that in hand, a consultation with a surgeon becomes far more productive, and it is one of the things an experienced practice will ask for, as covered in the guidance on choosing a surgeon for male body contouring.

The takeaway. Gynecomastia is common, it is almost always benign, and in most men it comes down to a life stage, a drug, a steroid cycle, or a treatable medical condition tilting the estrogen to testosterone balance. Finding the cause is worth the extra appointment: it can spare a young man an unnecessary operation, reverse an early medication-driven case, and, when surgery is the right answer, make the result more likely to last.

Related reading: Gynecomastia surgery and male breast reduction, explained.