Merck Manual

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Irvin H. Hirsch

, MD, Sidney Kimmel Medical College of Thomas Jefferson University

Reviewed/Revised Feb 2023
Topic Resources

Gynecomastia is hypertrophy of breast glandular tissue in males. It must be differentiated from pseudogynecomastia, which is increased breast fat, but no enlargement of breast glandular tissue.

Pathophysiology of Gynecomastia

During infancy and puberty, enlargement of the male breast is normal (physiologic gynecomastia). Enlargement is usually transient, bilateral, smooth, firm, and symmetrically distributed under the areola; breasts may be tender. Physiologic gynecomastia that develops during puberty usually resolves within about 6 months to 2 years. Similar changes may occur during old age and may be unilateral or bilateral. Most of the enlargement is due to proliferation of stroma, not of breast ducts. The mechanism is usually a decrease in androgen effect or an increase in estrogen effect (eg, decrease in androgen production, increase in estrogen production, androgen blockade, displacement of estrogen from sex-hormone binding globulin, androgen receptor defects).

Pearls & Pitfalls

  • During infancy and puberty, bilateral, symmetric, smooth, firm, and tender enlargement of breast tissue under the areola is normal.

If evaluation reveals no cause for gynecomastia, it is considered idiopathic. The cause may not be found because gynecomastia is physiologic or because there is no longer any evidence of the inciting event.

Etiology of Gynecomastia

In infants and boys, the most common cause is

  • Physiologic gynecomastia

In men, the most common causes are (see table )

  • Persistent pubertal gynecomastia

  • Idiopathic gynecomastia

  • Drugs (particularly spironolactone, anabolic steroids, and antiandrogens—see table )

Breast cancer, which is uncommon in males, may cause unilateral breast abnormalities but is rarely confused with gynecomastia.


Evaluation of Gynecomastia


History of present illness should help clarify the duration of breast enlargement, whether secondary sexual characteristics are fully developed, the relationship between onset of gynecomastia and puberty, and the presence of any genital symptoms (eg, decreased libido Libido There are 4 main components of male sexual function: Libido Erection Ejaculation Orgasm read more , erectile dysfunction Erectile Dysfunction Erectile dysfunction is the inability to attain or sustain an erection satisfactory for sexual intercourse. Most erectile dysfunction is related to vascular, neurologic, psychologic, and hormonal... read more ) and breast symptoms (eg, pain, nipple discharge).

Review of systems should seek symptoms that suggest possible causes, such as

Past medical history should address disorders that can cause gynecomastia and include a history of all prescribed and over-the-counter drugs.

Physical examination

Complete examination is done, including assessment of vital signs, skin, and general appearance. The neck is examined for goiter Simple Nontoxic Goiter Simple nontoxic goiter, which may be diffuse or nodular, is noncancerous hypertrophy of the thyroid without hyperthyroidism, hypothyroidism, or inflammation. Except in severe iodine deficiency... read more . The abdomen is examined for ascites Ascites Ascites is free fluid in the peritoneal cavity. The most common cause is portal hypertension. Symptoms usually result from abdominal distention. Diagnosis is based on physical examination and... read more , venous distention, and masses. Development of secondary sexual characteristics (eg, the penis, pubic hair, and axillary hair) is assessed. The testes are examined for masses or atrophy.

The breasts are examined while patients are recumbent with their hands behind the head. Examiners bring their thumb and forefinger together from opposite sides of the nipple until they meet. Any nipple discharge is noted. Lumps are assessed and characterized in terms of location, consistency, fixation to underlying tissues, and skin changes. Differentiation of true masses from accumulation of fatty tissue is detected by mammography or ultrasound imaging. The axilla is examined for lymph node involvement in men who have breast lumps.

Red flags

Interpretation of findings

With pseudogynecomastia, the examiner feels no resistance between the thumb and forefinger until they meet at the nipple. In contrast, with gynecomastia, a rim of tissue > 0.5 cm in diameter surrounds the nipple symmetrically and is similar in consistency to the nipple itself. Breast cancer is suggested by swelling with any of the following characteristics:

  • Eccentric unilateral location

  • Firm or hard consistency

  • Fixation to skin or fascia

  • Nipple discharge

  • Skin dimpling

  • Nipple retraction

  • Axillary lymph node involvement

Gynecomastia in an adult that is of recent onset and causes pain is more often caused by a hormonal abnormality (eg, tumor, hypogonadism) or drugs. Other examination findings may also be helpful (see ).



If breast cancer is suspected, mammography should be done. If another disorder is suspected, appropriate testing should be done (see table Some Causes of Gynecomastia Some Causes of Gynecomastia Some Causes of Gynecomastia ). Extensive testing is often unnecessary, especially for patients in whom the gynecomastia is chronic and detected only during physical examination. Because hypogonadism Male Hypogonadism Hypogonadism is defined as testosterone deficiency with associated symptoms or signs, deficiency of spermatozoa production, or both. It may result from a disorder of the testes (primary hypogonadism)... read more is somewhat common with aging, some authorities recommend measuring the serum testosterone level in older men, particularly if other findings suggest hypogonadism. However, in adults with recent onset of painful gynecomastia without a drug or evident pathologic cause, measurement of serum levels of luteinizing hormone (LH), follicle-stimulating hormone (FSH), testosterone, estradiol, and human chorionic gonadotropin (hCG) are recommended. Patients with physiologic or idiopathic gynecomastia are evaluated again in 6 months.

Treatment of Gynecomastia

In most cases, no specific treatment is needed because gynecomastia usually remits spontaneously or disappears after any causative drug (except perhaps anabolic steroids) is stopped or underlying disorder is treated. Some clinicians try tamoxifen 10 mg orally twice a day if pain and tenderness are very troublesome in men or adolescents, but this treatment is not always effective. Tamoxifen may also help prevent gynecomastia in men being treated with high-dose antiandrogen (eg, bicalutamide) therapy for prostate cancer; breast radiation therapy is an alternative. Resolution of gynecomastia with medical therapy is unlikely after 12 months (ie, late fibrotic stage). Thus, after 12 months, if cosmetic appearance is unacceptable, surgical removal of excess breast tissue (eg, suction lipectomy alone or with cosmetic surgery) may be used.

Key Points

  • Gynecomastia must be differentiated from increased fat tissue in the breast.

  • Gynecomastia is often physiologic or idiopathic.

  • A wide variety of drugs can cause gynecomastia.

  • Patients should be evaluated for clinically suspected genital or systemic disorders.

Drugs Mentioned In This Article

Drug Name Select Trade
Aldactone, CAROSPIR
Novarel, Ovidrel, Pregnyl
Nolvadex, Soltamox
NOTE: This is the Professional Version. CONSUMERS: View Consumer Version
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