Gynecomastia in Men: What Causes Breast Tissue Growth and When to Get It Checked

Finding new fullness or a firm lump behind your nipple is unsettling, and it is also common. Gynecomastia, the medical term for enlarged glandular tissue in the male breast, affects a large share of men at some point, most often around puberty and again later in life. Most cases are benign and tied to an ordinary shift in the balance between estrogen and testosterone. Still, it is worth understanding what is actually happening, what causes it, and which signs mean you should not wait to get it checked.

What gynecomastia actually is

Breast tissue in men responds to the same hormones it does in women, just in much smaller amounts. Estrogen stimulates glandular growth, and testosterone opposes it. When that balance tips toward more estrogen activity or less androgen activity, glandular tissue can grow, usually starting as a firm, sometimes tender area directly under the nipple. According to a review in the New England Journal of Medicine, this imbalance is the mechanism behind nearly every case of gynecomastia, whatever triggers it (https://doi.org/10.1056/NEJMcp070677).

It is worth separating true gynecomastia from pseudogynecomastia, which is simply fat accumulation in the chest from weight gain. On exam, true glandular tissue feels firm or rubbery and sits concentrically under the nipple, while fatty enlargement feels soft and spreads more diffusely across the chest. Mayo Clinic researchers note that distinguishing the two with a careful history and exam is the first and most useful step in any evaluation, often making further testing unnecessary (https://doi.org/10.1016/S0025-6196(11)60671-X).

The common, usually benign causes

Gynecomastia tends to show up at three points in life. Newborns can have transient breast tissue from maternal hormones that resolves within weeks. Many adolescent boys develop it during puberty, when estrogen rises faster than testosterone for a stretch of time; this pubertal gynecomastia typically fades within six months to two years without treatment. And a meaningful share of older men develop it as testosterone production declines with age while body fat, which converts testosterone to estrogen through an enzyme called aromatase, tends to increase. A review in Nature Reviews Endocrinology describes this as a predictable consequence of the androgen-to-estrogen ratio shifting with age and adiposity (https://doi.org/10.1038/nrendo.2014.139).

Medications are another frequent and fixable cause. Spironolactone, used for blood pressure and fluid retention, is one of the most common offenders. Anti-androgen therapy used to treat prostate cancer, specifically androgen deprivation therapy, causes gynecomastia in a substantial number of men, and a review in European Urology found that tamoxifen or prophylactic low-dose breast radiation can reduce that risk when ADT is being considered for prostate cancer treatment (https://doi.org/10.1016/j.eururo.2014.07.010). Some antipsychotics, certain ulcer medications, and recreational use of marijuana or alcohol have also been linked to breast tissue growth.

Anabolic steroid use deserves its own mention. Men who use anabolic-androgenic steroids, often to build muscle, can develop gynecomastia both from the steroids themselves converting to estrogen and from the testicular shutdown that follows stopping them, a pattern reviewed in Fertility and Sterility as anabolic steroid-induced hypogonadism (https://doi.org/10.1016/j.fertnstert.2014.02.002). If you have used performance-enhancing drugs, telling your clinician matters more for getting the right workup than it does for anything else.

Less common but important causes to rule out

Hyperthyroidism, liver disease, kidney disease, and primary or secondary hypogonadism can all disrupt the estrogen-testosterone balance enough to cause breast growth. Rarely, a hormone-secreting tumor of the testis, adrenal gland, or pituitary is responsible. These are uncommon, but they are part of why a clinician will usually ask about other symptoms, not just the breast change itself, and may order bloodwork such as testosterone, LH, estradiol, TSH, and liver function depending on what the history suggests.

When to get it checked promptly

Most gynecomastia is not an emergency, but a few features should move you to seek evaluation sooner rather than later: a lump that is hard or fixed in place rather than mobile, swelling limited to one side only, nipple discharge, skin puckering or dimpling, or a new lump under the arm. Male breast cancer is rare, but these are the findings that distinguish it from ordinary gynecomastia, and they are worth having a clinician look at directly.

What evaluation and treatment look like

A visit usually starts with questions about when the change started, how fast it has grown, every medication and supplement you take, and alcohol or substance use. A physical exam helps confirm whether this is glandular tissue or fat and whether anything looks concerning. From there, bloodwork or imaging such as ultrasound may be ordered depending on what the history points to.

Treatment follows the cause. If a medication is responsible, adjusting or switching it, with your prescribing clinician's guidance, often resolves it over time. If low testosterone, thyroid disease, or another hormonal condition is found, treating that condition is the priority. For gynecomastia caught early, while the tissue is still in an active, more glandular phase rather than fibrous and scarred, medications such as tamoxifen have shown benefit in some studies, though the evidence here is mostly from smaller trials and specific clinical scenarios like ADT-related gynecomastia rather than large randomized trials across all causes. Gynecomastia that has been present for more than a year, when the tissue has often become more fibrotic, responds less reliably to medication, and surgical removal becomes the more realistic option for men who want it resolved.

Weight loss helps the fatty component of chest enlargement but will not shrink true glandular tissue on its own, which is why getting an accurate diagnosis up front matters before assuming diet and exercise will take care of it.

Getting evaluated

If you have noticed new breast tissue, tenderness, or asymmetry, that is a reasonable reason to be seen, not something to just monitor indefinitely on your own. We see this regularly in men's health visits and can walk through your history, medications, and next steps, including bloodwork or imaging when it is warranted. Most major insurance plans are accepted, including Medicare, so getting this looked at does not have to mean paying out of pocket on top of the coverage you already have.