ByIrvin H. Hirsch, MD, Sidney Kimmel Medical College of Thomas Jefferson University
Reviewed/Revised Feb 2023
View Patient Education

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 Some Causes of Gynecomastia)

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, erectile dysfunction) and breast symptoms (eg, pain, nipple discharge).

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

  • Weight loss and fatigue (cirrhosis, undernutrition, chronic kidney disease, hyperthyroidism)

  • Skin discoloration (chronic kidney disease, cirrhosis)

  • Hair loss and frequent infections (undernutrition)

  • Fragility fractures (undernutrition, hypogonadism)

  • Mood and cognitive changes (hypogonadism)

  • Tremor, heat intolerance, and diarrhea (hyperthyroidism)

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. The abdomen is examined for ascites, 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

The following findings are of particular concern:

  • Localized or eccentric breast swelling, particularly with nipple discharge, fixation to the skin, or hard consistency

  • Symptoms or signs of hypogonadism (eg, delayed puberty, testicular atrophy, decreased libido, erectile dysfunction, decreased proportion of lean body mass, loss of visual-spatial abilities)

  • Symptoms or signs of hyperthyroidism (eg, tremor, tachycardia, sweating, heat intolerance, weight loss)

  • Testicular mass

  • Recent onset of painful, tender gynecomastia in an adult

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 Interpretation of Some Findings in Gynecomastia).



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). Extensive testing is often unnecessary, especially for patients in whom the gynecomastia is chronic and detected only during physical examination. Because hypogonadism 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

Treatment of Gynecomastia

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
Test your KnowledgeTake a Quiz!
Download the free Merck Manual App iOS ANDROID
Download the free Merck Manual App iOS ANDROID
Download the free Merck Manual App iOS ANDROID