In this guide18 sections
- Key Points
- What Is Gynecomastia (Gyno) in Men?
- What Causes Gyno? The Hormone Balance Explained
- What Causes Gynecomastia at Different Ages?
- What Is the Most Common Cause of Gynecomastia?
- Which Medications Cause Gynecomastia?
- Do Steroids Cause Gyno? Steroids, SARMs and Supplements
- Can Cannabis and Alcohol Cause Gynecomastia?
- Does Being Overweight Cause Gynecomastia?
- Which Medical Conditions Cause Gynecomastia?
- Is Gynecomastia Genetic?
- What Causes Gynecomastia on One Side?
- Why Is Gynecomastia Sore or Tender at First?
- When Should You See a Doctor About Gynecomastia?
- Can Gynecomastia Go Away If the Cause Is Treated?
- Frequently Asked Questions
- Why Choose Centre for Surgery for Gynecomastia Surgery?
- References
Key Points
- Gynecomastia is caused by a shift in the balance between oestrogen and testosterone. Oestrogen makes male breast tissue grow and androgens hold it back, so anything that raises one or lowers the other can cause gyno.
- In most young men no single cause is found. In a 2026 study of 19,640 boys and young men, almost three quarters of cases were idiopathic, about a quarter were linked to medication and only 3% were caused by an underlying illness.
- Puberty is the most common trigger. Around half of boys develop some breast tissue in mid-puberty, and in more than nine out of ten it settles within two years.
- Medicines, steroids and drugs matter. Medicines are thought to cause 10% to 25% of all cases, and anabolic steroids, cannabis and alcohol are all linked with gyno.
- Some causes need checking first. A new, one-sided, hard or growing lump in an adult man, or any change in the testicles, should be seen by a GP before anyone talks about surgery.
- Treating the cause helps early, not late. Once breast tissue has been present for a year or more it becomes firmer and rarely shrinks on its own, which is when surgery is usually considered.
Most men who search for what causes gyno want to know two things: why it has happened to them, and whether it means something is wrong. The honest answer is that gynecomastia almost always comes down to hormones, that most cases are harmless, and that a small number have a cause worth finding. This guide explains each of the causes of gynecomastia in men, from puberty and weight to medicines, steroids, cannabis and medical conditions, and how to tell when it is worth seeing a doctor.
If you are not yet sure whether your chest is gland or fat, our guide to gynecomastia vs chest fat is a good place to start, and our article on what gynecomastia feels like describes the typical lump under the nipple.
What Is Gynecomastia (Gyno) in Men?
Gynecomastia is a benign growth of the glandular tissue of the male breast.[1] Gyno is simply its short name, and man boobs is the everyday phrase people use for an enlarged male chest, whatever its cause. True gynecomastia is a firm or rubbery disc of tissue sitting directly behind the nipple. It is different from pseudogynecomastia, where the chest is enlarged by fat alone, although many men have a mixture of both.
The distinction matters for causes. Fat responds to weight loss, but gland does not, and the things that make gland grow are almost all hormonal.
What Causes Gyno? The Hormone Balance Explained
Every man produces some oestrogen. Oestrogen stimulates breast tissue to grow, while testosterone and other androgens hold that growth back. Most cases of gynecomastia result from too much oestrogen action, too little androgen action, or both, acting on the breast tissue.[2]
That balance can shift in several ways:
- More oestrogen being made. An enzyme called aromatase turns testosterone into oestradiol. It is found in fat tissue, so more body fat means more conversion. Some tumours also make oestrogen or hCG, a hormone that drives oestrogen production in the testicles.
- Less testosterone being made. This happens with ageing, testicular problems, some pituitary conditions and after anabolic steroid use, when the body’s own production is switched off.
- Testosterone being blocked. Some medicines stop testosterone working on its receptor, or stop it being converted to its more active form.
- Changes in carrier proteins. More testosterone than oestrogen is bound to a protein called SHBG, so conditions that raise SHBG, such as liver disease and an overactive thyroid, leave relatively more free oestrogen.
This is also why high testosterone can cause gyno. When testosterone is taken in large doses, as in a steroid cycle or poorly monitored testosterone therapy, a share of it is converted into oestradiol, and the breast tissue responds.
What Causes Gynecomastia at Different Ages?
Gynecomastia has three natural peaks: in newborn babies, in teenage boys and in older men. A CT study of 506 men in Academic Radiology found the highest rates of breast tissue enlargement in boys aged 13 to 14 and in men in their eighties.[3] Our guide to how common gynecomastia is covers the figures at each age in more detail.
Newborn babies
Many newborn boys have small breast buds from their mother’s oestrogen crossing the placenta. This is normal and usually settles within the first year of life.[1]
Teenage boys and puberty
During puberty, oestrogen levels can rise before testosterone fully catches up. The European Academy of Andrology guidelines ↗ state that pubertal gynecomastia affects around half of mid-pubertal boys, and that it resolves on its own within 24 months in more than 90% of cases.[1] Our guide to whether gynecomastia goes away on its own explains what to expect, and our teenage gynecomastia page explains when surgery is considered for younger patients.
Adult men
Gyno that starts in adulthood is more likely to have an identifiable cause. The same guidelines note that a proper investigation finds an underlying cause in roughly 45% to 50% of adult cases, most often a medicine, a substance or a hormone problem.[1]
Older men
Testosterone falls gradually with age while body fat, and the aromatase it contains, tends to rise. Older men are also more likely to take medicines linked with gyno and to have liver or kidney disease, so gynecomastia becomes more common again from middle age onwards.
What Is the Most Common Cause of Gynecomastia?
For most men, no specific cause is ever found. The largest recent study, a 2026 population study of 19,640 males aged 10 to 25 in JPRAS Open ↗, classified 74.3% of cases as idiopathic, meaning no cause was found, 23.1% as medication-related and only 3.4% as caused by an underlying illness.[4] Obesity and family history were the main factors in younger boys, while older adolescents were more likely to have a secondary cause.
Being told your gyno is idiopathic is not a reason to worry. Most idiopathic gynecomastia is pubertal tissue that never fully regressed, which is why so many men say they have had gyno since they were teenagers.
Which Medications Cause Gynecomastia?
Medicines are estimated to cause 10% to 25% of all cases of gynecomastia.[5] An evidence review in Expert Opinion on Drug Safety graded each reported link and found that most rest on weak evidence, but that some drugs are definitely associated with gyno and others probably are.[5]
| Strength of link | Medicines |
|---|---|
| Definite | Spironolactone, cimetidine, ketoconazole, growth hormone, oestrogens, hCG, anti-androgens used for prostate cancer, GnRH analogues and 5-alpha reductase inhibitors such as finasteride and dutasteride |
| Probable | Risperidone, verapamil, nifedipine, omeprazole, some chemotherapy drugs, efavirenz for HIV, anabolic steroids, alcohol and opioids |
If you take finasteride for hair loss, our guide to finasteride gynecomastia explains how often it happens and what to do. The evidence for antidepressants is weaker and is covered in can antidepressants cause gynecomastia?
Never stop a prescribed medicine on your own. Speak to the doctor who prescribed it, who can weigh up whether an alternative is suitable. Gyno caused by a medicine often improves after it is stopped, particularly if the tissue is still tender and has been present for less than a year.
Do Steroids Cause Gyno? Steroids, SARMs and Supplements
Anabolic steroids are one of the clearest causes of gynecomastia in otherwise healthy young men. Large doses of testosterone and aromatising steroids are partly converted into oestradiol, and every steroid cycle switches off the body’s own testosterone production. Even steroids marketed as non-aromatising, such as oxandrolone (Anavar) or stanozolol (Winstrol), suppress natural testosterone, and the hormone crash at the end of a cycle can tip the balance towards oestrogen.
The numbers are significant. In the HAARLEM study, which followed 100 men through a self-chosen steroid cycle, gynecomastia was observed in 19% of them.[6] Steroid use is also under-reported. When one plastic surgery unit asked its gynecomastia patients again three months after surgery, the proportion admitting steroid use rose from 4% before the operation to 39%.[7] In a separate series of 964 men having gynecomastia surgery, steroid users needed revision surgery more often than non-users.[8]
Prohormones, SARMs and some unlicensed gym supplements can have similar effects, and products bought online are sometimes contaminated with steroids that are not on the label. Our guides to steroids and gynecomastia and bodybuilder gynecomastia go into more detail, and why gyno affects even fit men explains why training cannot shift gland once it has formed.
Can Cannabis and Alcohol Cause Gynecomastia?
Cannabis has long been suspected, and the evidence is growing, although it still shows an association rather than proof. A 2022 chest CT study in Radiology ↗ found gynecomastia in 38% of male cannabis smokers, compared with 16% of non-smokers and 11% of tobacco-only smokers.[9] In an Italian clinic study of more than 4,000 men, gynecomastia was also linked with cannabis use, along with low testosterone, testicular disease and liver disease.[10] Our article can cannabis cause gynecomastia? looks at the evidence in full.
Heavy drinking is a probable cause in its own right.[5] Alcohol increases the conversion of testosterone to oestrogen and, over time, damages the liver, which normally clears oestrogen from the blood.
Does Being Overweight Cause Gynecomastia?
Excess weight contributes in two ways. Fat tissue contains aromatase, so more fat means more oestrogen, and fat also enlarges the chest directly. In the 2026 study, obesity was one of the main factors in younger boys with gyno, and morbidly obese patients were more likely to need surgery.[4]
Weight is not the whole story, though. Two CT studies, one of 506 men and one of 5,501 men, found that the amount of true breast gland did not correlate with body mass index.[3][11] Much of what looks like gyno in heavier men is chest fat, which is why it shrinks with weight loss when true gland does not. If you carry fat around the chest without being heavy overall, our guides to skinny fat and whether exercise prevents gynecomastia may help.
Which Medical Conditions Cause Gynecomastia?
A minority of cases are caused by an underlying condition, which is why adult-onset gyno deserves a check.[1][2] The main ones are:
- Liver disease. Cirrhosis reduces the breakdown of oestrogen and raises SHBG. Men with cirrhosis have markedly more breast gland on CT.[3]
- Chronic kidney disease. Kidney disease at every stage, and dialysis, are linked with gynecomastia.[11]
- Low testosterone (hypogonadism). This includes Klinefelter syndrome, testicular damage from injury, infection or mumps, and pituitary problems.
- An overactive thyroid. Hyperthyroidism raises SHBG and oestrogen production, and gyno often settles once the thyroid is treated.
- Tumours that make hormones. These are rare, but testicular tumours, some adrenal tumours and, very occasionally, lung cancers that produce hCG can all cause gynecomastia. A testicular tumour can be small enough to miss by touch, so the guidelines recommend a testicular ultrasound when gyno needs investigating.[1]
- Recovery from malnutrition. Regaining weight after a period of starvation or serious illness can trigger gynecomastia as hormone production restarts.
Gynecomastia itself is not a cancer and does not turn into one. The guidelines are clear that it should not be considered a pre-cancerous condition.[1] Our article on whether gynecomastia increases breast cancer risk explains how the two are told apart.
Is Gynecomastia Genetic?
It can run in families. In the 2026 study, men with two or more affected brothers were more than eight times as likely to need surgery, and familial cases were most common in younger boys.[4] Rare inherited conditions, such as aromatase excess syndrome and Klinefelter syndrome, cause gynecomastia directly, but for most men a family pattern simply reflects inherited sensitivity of the breast tissue to normal hormone levels.
What Causes Gynecomastia on One Side?
One-sided gyno usually has the same causes as gyno on both sides. The two breasts simply respond at different speeds, and in the CT study of 5,501 men, more than a third of those with gynecomastia had it on one side only.[11] Our guide to unilateral gynecomastia explains this in detail.
A hard, fixed lump that is off-centre from the nipple, or one with skin changes or discharge, is different and should always be checked by a GP. If the main change is a soft, raised areola, our guide to puffy nipples may be more relevant.
Why Is Gynecomastia Sore or Tender at First?
New gynecomastia is often tender or sensitive. In the early phase the gland tissue is actively growing, and this is also the stage when removing the cause, such as stopping a medicine or a steroid cycle, is most likely to work. After around a year the tissue tends to become firmer and more fibrous, which is why long-standing gyno rarely shrinks on its own even when the original cause has gone. Our guide to gynecomastia grades explains how the amount of gland and skin affects treatment.
When Should You See a Doctor About Gynecomastia?
See your GP if:
- the swelling is on one side only and feels hard, fixed or off-centre from the nipple
- there is nipple discharge, bleeding, skin dimpling or a change in the nipple
- the breast is growing quickly or is painful
- you notice a lump, swelling or change in either testicle
- gyno has started in adulthood without an obvious reason, such as a new medicine or steroid use
A doctor will ask about medicines, supplements, drugs and alcohol, examine the chest and testicles, and may arrange blood tests. The European guidelines suggest testosterone, oestradiol, SHBG, LH, FSH, thyroid function, prolactin, hCG, AFP, and liver and kidney tests, with breast imaging if the examination is unclear.[1]
Can Gynecomastia Go Away If the Cause Is Treated?
Often, if it is caught early. The guidelines recommend watchful waiting after an underlying condition has been treated or a medicine or substance has been stopped.[1] They do not recommend tablets such as tamoxifen or aromatase inhibitors as a general treatment, and suggest surgery for gynecomastia that has lasted a long time and has not regressed.[1] Our guide to non-surgical gynecomastia treatments covers what can and cannot help.
When gyno is established, gynecomastia surgery removes the gland and any excess fat through small incisions, usually with VASER or power-assisted liposuction. Our guides to gynecomastia surgery cost, gynecomastia recovery and whether gyno surgery is worth it explain the next steps. If the cause, such as steroid use, continues after surgery, gland can regrow, as explained in can gynecomastia come back after surgery?
Frequently Asked Questions
What causes gyno in teenage boys?
Usually puberty itself. Oestrogen rises before testosterone fully catches up, and around half of boys develop some breast tissue in mid-puberty. In more than 90% it settles within two years. Weight gain, family history and, less often, medicines, cannabis or steroids can also play a part.
Can high testosterone cause gyno?
Yes. When testosterone is taken in large amounts, part of it is converted into oestradiol by the aromatase enzyme, and the breast tissue responds. This is why gyno is common during and after steroid cycles and with poorly monitored testosterone therapy.
What hormone imbalance causes gynecomastia?
An imbalance where oestrogen action is too strong relative to androgen action in the breast. That can come from more oestrogen, less testosterone, testosterone being blocked, or a change in the proteins that carry these hormones in the blood.
Can stress or poor sleep cause gynecomastia?
There is no good evidence that stress or sleep cause gynecomastia directly. They can affect weight and hormone levels over time, but they are not recognised causes in medical guidelines.
Can certain foods cause gyno?
Not at normal amounts in a balanced diet. Soy and other foods containing plant oestrogens are often blamed online, but gynecomastia from food has only been reported with very unusual, very high intakes. Excess calories matter more, through weight gain.
Can masturbation cause gynecomastia?
No. This is a common myth, and there is no link between masturbation and gynecomastia.
Is gynecomastia dangerous?
Gynecomastia itself is benign and is not a pre-cancerous condition. What matters is the occasional underlying cause, which is why new gyno in an adult, or a hard one-sided lump, should be checked by a doctor.
Will gyno go away if I stop the cause?
It is most likely to improve if the tissue is still tender and has been present for less than about a year. Long-standing gyno has usually become fibrous and rarely shrinks without surgery.
Why Choose Centre for Surgery for Gynecomastia Surgery?
We treat every grade of gynecomastia, including grade 3 to 4 and revision cases after surgery elsewhere, with VASER or power-assisted liposuction and gland removal matched to your chest. Surgery is performed by GMC-registered plastic surgeons at our CQC-regulated hospital at 95–97 Baker Street, which has been caring for patients for over 10 years, and the surgeon who examines you at consultation is the surgeon who performs your operation. At consultation your surgeon will ask about medicines, supplements and steroid use, and will recommend a GP or specialist review first if anything suggests an underlying cause. When you are asleep, your anaesthetic is TIVA given by a consultant anaesthetist, and almost all of our operations are day cases. You can see real results in our gynecomastia before and after photos, and our other options for men are on our surgery for men page. We recommend a two-week cooling-off period before any surgery, and we publish our clinical outcomes and patient safety data.
Finance is available through Chrysalis Finance, subject to status. See our finance options page for details.
Phone: 020 7993 4849 | Address: 95–97 Baker Street, Marylebone, London W1U 6RN
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References
- Kanakis GA, Nordkap L, Bang AK, et al. EAA clinical practice guidelines: gynecomastia evaluation and management. Andrology 2019;7(6):778–793. doi:10.1111/andr.12636 ↗
- Narula HS, Carlson HE. Gynaecomastia: pathophysiology, diagnosis and treatment. Nature Reviews Endocrinology 2014;10(11):684–698. doi:10.1038/nrendo.2014.139 ↗
- Klang E, Kanana N, Grossman A, et al. Quantitative CT assessment of gynecomastia in the general population and in dialysis, cirrhotic, and obese patients. Academic Radiology 2018;25(5):626–635. doi:10.1016/j.acra.2017.11.008 ↗
- Hilewitz D, Tsion GB, Ad-El D, et al. A retrospective population-based analysis of 19,640 pediatric and young adult males with gynecomastia. JPRAS Open 2026;49:595–606. doi:10.1016/j.jpra.2026.03.025 ↗
- Deepinder F, Braunstein GD. Drug-induced gynecomastia: an evidence-based review. Expert Opinion on Drug Safety 2012;11(5):779–795. doi:10.1517/14740338.2012.712109 ↗
- Smit DL, Buijs MM, de Hon O, den Heijer M, de Ronde W. Positive and negative side effects of androgen abuse. The HAARLEM study: a one-year prospective cohort study in 100 men. Scandinavian Journal of Medicine & Science in Sports 2021;31(2):427–438. doi:10.1111/sms.13843 ↗
- Beniwal M, Singh K, Singh P, Sharma A, Beniwal S. The burden of anabolic androgenic steroid-induced gynecomastia. Indian Journal of Plastic Surgery 2023;56(4):338–343. doi:10.1055/s-0043-1771293 ↗
- Vojvodic M, Xu FZ, Cai R, Roy M, Fielding JC. Anabolic-androgenic steroid use among gynecomastia patients: prevalence and relevance to surgical management. Annals of Plastic Surgery 2019;83(3):258–263. doi:10.1097/SAP.0000000000001850 ↗
- Murtha L, Sathiadoss P, Salameh JP, Mcinnes MDF, Revah G. Chest CT findings in marijuana smokers. Radiology 2023;307(1):e212611. doi:10.1148/radiol.212611 ↗
- Maseroli E, Rastrelli G, Corona G, et al. Gynecomastia in subjects with sexual dysfunction. Journal of Endocrinological Investigation 2014;37(6):525–532. doi:10.1007/s40618-014-0055-z ↗
- Kim MS, Kim JH, Lee KH, Suh YJ. Incidental gynecomastia on thoracic computed tomography in clinical practice: characteristics, radiologic features, and correlation with possible causes in South Korean men. American Journal of Men’s Health 2020;14(3):1557988320908102. doi:10.1177/1557988320908102 ↗
