Low testosterone can cause man boobs — a condition clinically known as gynaecomastia — by disrupting the balance between testosterone and oestrogen in the male body. When testosterone levels fall, the relative dominance of oestrogen increases, stimulating the growth of glandular breast tissue. This hormonal shift can occur due to ageing, obesity, certain medications, or underlying health conditions. Understanding why this happens, when to seek medical advice, and what treatment options are available on the NHS is essential for any man experiencing unexplained breast changes or symptoms of testosterone deficiency.

How Low Testosterone Can Lead to Gynaecomastia

Low testosterone reduces its suppressive effect on breast tissue, allowing oestrogen to stimulate glandular growth; it is the shift in the oestrogen-to-testosterone ratio that drives gynaecomastia, not a change in either hormone in isolation.

Gynaecomastia — the development of enlarged glandular breast tissue in men — affects a significant number of males at various stages of life. One of the key hormonal drivers behind this condition is low testosterone, a state clinically referred to as hypogonadism or testosterone deficiency. Understanding how this hormonal imbalance contributes to breast tissue growth is important for both patients and clinicians.

Testosterone and oestrogen are both present in the male body, but under normal circumstances, testosterone is dominant. When testosterone levels fall — whether due to ageing, illness, or other factors — the relative proportion of oestrogen increases. It is this shift in the oestrogen-to-testosterone ratio, rather than a change in either hormone in isolation, that can stimulate the proliferation of glandular breast tissue in men. It is worth noting that absolute increases in oestrogen — for example, from oestrogen-secreting tumours, exogenous oestrogen exposure, or human chorionic gonadotrophin (hCG)-secreting tumours — can also cause gynaecomastia independently of low testosterone.

The mechanism involves oestrogen binding to receptors in breast tissue, promoting cellular growth in the ductal and stromal components of the gland. Individual sensitivity of breast tissue receptors and the overall degree of hormonal imbalance both influence whether gynaecomastia develops; not every man with a degree of testosterone decline will experience visible breast enlargement. It is important to distinguish true gynaecomastia (glandular tissue growth) from pseudogynaecomastia, which refers to fat accumulation in the chest area without glandular involvement — a distinction with direct implications for diagnosis and treatment.

For further information, see the NHS page on breast enlargement (gynaecomastia) in men and the NICE Clinical Knowledge Summary (CKS) on gynaecomastia.

Understanding the Link Between Hormones and Breast Tissue in Men

Oestrogen promotes breast tissue growth in men via aromatase conversion of testosterone in fat tissue; obesity and ageing increase this conversion, compounding the effects of low testosterone.

The male breast, though largely undeveloped compared to the female breast, contains hormone-sensitive tissue that responds to circulating sex hormones throughout a man's life. Testosterone generally suppresses breast tissue development, whilst oestrogen — primarily oestradiol in men — promotes it. This hormonal interplay is tightly regulated under healthy conditions.

In men, oestrogen is produced in small quantities by the testes and adrenal glands, but a significant proportion is derived from the peripheral conversion of androgens (including testosterone) into oestrogens via an enzyme called aromatase. This process occurs predominantly in adipose (fat) tissue. Aromatase activity is increased by higher body fat and by ageing, meaning that men who are overweight or older tend to produce more oestrogen through this pathway — which can compound the effects of low testosterone.

When testosterone levels decline, the suppressive effect on breast tissue is reduced. In men with excess body fat, increased aromatase activity may simultaneously raise oestradiol production, further shifting the hormonal balance. This dual mechanism helps explain why gynaecomastia is more prevalent in older men and those who are overweight. However, not all men with low testosterone will develop gynaecomastia, as individual receptor sensitivity and the overall degree of hormonal imbalance both influence outcomes.

Relevant UK clinical context is provided in the NICE CKS on gynaecomastia and in guidance from the Society for Endocrinology and the British Society for Sexual Medicine (BSSM) on male hypogonadism.

Common Causes of Low Testosterone and Gynaecomastia in the UK

Common causes include age-related testosterone decline, obesity, medications such as spironolactone and anabolic steroids, liver disease, hypogonadism, and hCG-secreting testicular tumours.

In the UK, low testosterone and associated gynaecomastia arise from a range of underlying causes, some physiological and others pathological. Awareness of these causes helps clinicians identify the most appropriate investigations and management strategies.

Common causes include:

• Age-related decline: Testosterone levels naturally decrease by approximately 1% per year after the age of 30–40, making age-related gynaecomastia relatively common in middle-aged and older men.

• Obesity: Excess adipose tissue increases aromatase activity, raising oestrogen levels and lowering the testosterone-to-oestrogen ratio.

• Medications: Several commonly prescribed drugs can lower testosterone or raise oestrogen. These include spironolactone, cimetidine, digoxin, ketoconazole, some antipsychotics, anti-androgens (e.g., cyproterone acetate, bicalutamide), 5-alpha-reductase inhibitors (finasteride, dutasteride), GnRH analogues, antiretrovirals, opioids, anabolic steroids (paradoxically, through suppression of natural testosterone production), and certain chemotherapy agents. For authoritative information on medicine-associated adverse effects, consult individual Summary of Product Characteristics (SmPCs) via the electronic Medicines Compendium (emc), the British National Formulary (BNF), and relevant MHRA Drug Safety Updates. Suspected adverse drug reactions should be reported via the MHRA Yellow Card scheme (yellowcard.mhra.gov.uk).

• Chronic conditions: Liver disease, chronic kidney disease, and hyperthyroidism can all disrupt hormonal metabolism and contribute to gynaecomastia.

• Hypogonadism: Primary hypogonadism (testicular failure) or secondary hypogonadism (pituitary or hypothalamic dysfunction) directly reduces testosterone production.

• Tumours: hCG-secreting testicular germ cell tumours are an important cause of gynaecomastia in younger men and must be excluded. Adrenal tumours and other hormone-secreting neoplasms are rarer but recognised causes.

• Klinefelter syndrome: A genetic condition (47,XXY) associated with testicular insufficiency and an elevated risk of gynaecomastia.

In some cases, no identifiable cause is found — this is termed idiopathic gynaecomastia and is particularly common during puberty, when it typically resolves without intervention. See NICE CKS: Gynaecomastia and relevant BNF monographs for further detail.

When to See a GP About Hormonal Changes and Chest Swelling

See a GP promptly for any new breast lump, nipple discharge, or rapid breast enlargement; NICE NG12 recommends an urgent two-week-wait referral if male breast cancer cannot be excluded.

Many men feel embarrassed or uncertain about seeking medical advice for breast changes, yet early assessment is important to rule out serious underlying conditions and to access appropriate support. The NHS advises that any new or unexplained breast swelling in men should be evaluated by a GP.

Contact your GP promptly if you notice:

• A lump, swelling, or tenderness in one or both breasts

• Nipple discharge (particularly if bloodstained)

• Changes in the skin overlying the breast, such as dimpling or puckering

• Rapid or asymmetrical breast enlargement

• A new testicular lump, pain, or enlargement (which may indicate a tumour causing gynaecomastia)

• Symptoms of low testosterone, such as reduced libido, fatigue, low mood, or erectile dysfunction

Whilst gynaecomastia is usually benign, it is essential to exclude male breast cancer, which, although rare, accounts for approximately 1% of all breast cancer diagnoses in the UK. In line with NICE NG12 (Suspected cancer: recognition and referral), an urgent two-week-wait referral to a breast clinic should be made for:

• Men aged 30 and over with an unexplained breast lump

• Men aged 50 and over with unilateral nipple discharge, nipple retraction, or other suspicious nipple changes

• Anyone with a suspicious axillary lump

If you are taking any medication known to affect hormone levels and you notice breast changes, do not stop your medication without medical advice — instead, discuss your concerns with your GP or prescribing clinician. Hormonal symptoms such as persistent fatigue, mood changes, and reduced muscle mass alongside breast swelling may suggest an underlying endocrine disorder requiring further investigation.

See also: NHS page on breast enlargement (gynaecomastia) in men; NICE NG12.

Diagnosis and Treatment Options Available on the NHS

Diagnosis involves morning serum testosterone measured on two separate occasions, alongside LH, FSH, oestradiol, and imaging if indicated; treatment depends on the underlying cause and may include TRT, medication review, tamoxifen, or surgery.

When a patient presents with suspected gynaecomastia and possible low testosterone, the GP will typically begin with a thorough clinical history and physical examination. This includes reviewing current medications, assessing body mass index (BMI), and examining the breast tissue to differentiate glandular enlargement from fatty tissue.

Investigations may include:

• Blood tests: Serum total testosterone should be measured in the morning (ideally between 8am and 11am) on at least two separate occasions to confirm a consistently low result. Sex hormone-binding globulin (SHBG) and albumin should be measured alongside total testosterone to allow calculation of free (biologically active) testosterone when clinically indicated. Additional tests include luteinising hormone (LH), follicle-stimulating hormone (FSH), oestradiol, prolactin, thyroid function, liver function, and renal function. Beta-hCG and alpha-fetoprotein (AFP) should be measured when a testicular or other germ cell tumour is suspected.

• Imaging: Testicular ultrasound if a testicular cause is suspected; mammography or breast ultrasound if malignancy cannot be excluded on clinical grounds.

• Referral: To endocrinology for confirmed hypogonadism; to a breast clinic under NICE NG12 if cancer is suspected.

Treatment depends on the underlying cause:

• Where a causative medication is identified, switching or stopping it (under medical supervision) may resolve the gynaecomastia. Drug-induced gynaecomastia often improves within 3–12 months after withdrawal of the causative agent, though established glandular tissue may persist.

• If low testosterone is confirmed, testosterone replacement therapy (TRT) may be considered. TRT is indicated in men with consistently low morning testosterone levels alongside symptoms of deficiency, in the absence of contraindications. Contraindications include prostate cancer, male breast cancer, and certain haematological conditions. TRT suppresses spermatogenesis and can impair fertility; men who wish to father children should receive fertility counselling before starting treatment. TRT itself can sometimes increase oestrogen levels through aromatisation, and monitoring should include serum testosterone, haematocrit (to detect polycythaemia), and PSA (in men at risk of prostate disease). Other potential adverse effects include fluid retention, acne, and — paradoxically — gynaecomastia. TRT should be initiated and monitored in line with Society for Endocrinology or BSSM guidance on male hypogonadism.

• For recent-onset or painful gynaecomastia, specialist-led off-label medical therapy — most commonly tamoxifen — may be considered. This is a specialist decision and is not routinely available in primary care; refer to the BNF and local endocrinology guidance for further detail.

• In cases where gynaecomastia is longstanding or causing significant psychological distress, surgical referral for subcutaneous mastectomy may be considered, though NHS funding criteria vary by Integrated Care Board (ICB).

NICE does not currently have a dedicated guideline on gynaecomastia, but management broadly follows NICE CKS guidance and endocrinology and surgical best practice.

Lifestyle Changes and Medical Support for Managing Symptoms

Weight loss reduces aromatase activity and improves the testosterone-to-oestrogen ratio, while alcohol reduction and avoiding anabolic steroids support hormonal health; established glandular tissue may still require medical or surgical management.

Alongside medical treatment, lifestyle modifications can play a meaningful role in managing both low testosterone and gynaecomastia, particularly where obesity and metabolic health are contributing factors.

Evidence-supported lifestyle strategies include:

• Weight management: Reducing body fat through a balanced diet and regular physical activity can lower aromatase activity, improve the testosterone-to-oestrogen ratio, and reduce the appearance of chest enlargement. Even modest weight loss of 5–10% of body weight can have measurable hormonal benefits. However, established glandular breast tissue may not regress with weight loss alone and may require medical or surgical management.

• Resistance exercise: Strength training can support improvements in body composition, reducing visceral fat and pseudogynaecomastia. Whilst the effect of resistance training on testosterone levels is generally modest, the broader metabolic and cardiovascular benefits are well established.

• Alcohol reduction: Chronic alcohol use is associated with liver dysfunction and suppressed testosterone production. Reducing intake to within the UK Chief Medical Officers' low-risk drinking guideline — no more than 14 units per week, spread over three or more days, with several alcohol-free days — supports hormonal and liver health.

• Avoiding anabolic steroids and performance-enhancing drugs: These substances suppress the hypothalamic-pituitary-gonadal axis and are a well-recognised cause of gynaecomastia.

Mental health support is also an important consideration. Gynaecomastia can cause significant psychological distress, including low self-esteem, social withdrawal, and anxiety. Patients should be encouraged to discuss emotional impacts with their GP, who can refer to NHS Talking Therapies or other appropriate support services.

For men with confirmed testosterone deficiency, ongoing monitoring under the care of an endocrinologist or a GP with a special interest in men's health ensures that treatment remains safe and effective. Open communication with healthcare providers — and not delaying seeking help — remains the most important step towards managing symptoms and improving quality of life.

For further information and support, see the NHS page on breast enlargement (gynaecomastia) in men and the UK Chief Medical Officers' Low Risk Drinking Guidelines.

Frequently Asked Questions