Simply put, we can define gynecomastia as the abnormal enlargement of male breast tissue. Many men may be unaware that they have breast tissue – just like women. It is the balance of the ‘female’ hormone estrogen and the ‘male’ testosterone which control whether the breasts grows.

So, in most men, the higher level of testosterone tells the breasts not to grow, and they stay so small that the tissue cannot be seen, or in many cases even felt.

However, it is still there, and sits just behind the nipple. If the hormonal balance changes and the level of estrogen becomes relatively higher, this sends a message to the breast tissue to grow.

As this does not happen in most men and for most of the time, it is considered abnormal and is given the medical term ‘gynecomastia’. Men may think of themselves as having man-boobs or ‘gyno’.

Gynecomastia is very common at certain stages of life – so common it can almost be thought of as normal. For example, up to 70% of teenagers will have some degree of gyno at some point during puberty. For them the gyno definition still applies, but with time and patience most cases will go away on their own.

The surge of hormones during puberty causes the growth, and as this settles down the breast tissue returns to normal.

Gyno is also sometimes used to describe a man who develops boobs due to the build-up of fatty tissue in the breast area. Although this doesn’t strictly meet the gynecomastia definition as the breast itself may be normally sized, it can be very difficult to tell the difference.

In fact, in many men there is often a combination of breast tissue and fatty tissue that causes the swelling – so the gynecomastia definition still fits. When there is just fatty tissue causing the enlargement, the medical term is pseudogynecomastia.

normal breast and gynecomastia

Gynecomastia medical definition

The medical definition of gynecomastia is the abnormal enlargement of male breast tissue. In addition to this simple description a grading system has also been developed. This allows doctors to communicate clearly with each other, and also to track the progress of gynecomastia which may be getting bigger or smaller over time.

The grading system does not really have any meaning, other than providing a clear description. Each man will develop different sized man-boobs, even if high estrogen levels continue. Only a small number of men will develop very large breasts.

The medical definition of gyno stages or grades is given below:

  • Grade 1 – Minor breast enlargement localised behind the areola
  • Grade 2 – Minor to significant breast enlargement spreading beyond the areola with an indistinct edge blending with the chest wall
  • Grade 3 – Significant breast enlargement across the chest wall with a clear margin and redundant skin
  • Grade 4 – Significant breast enlargement with redundant skin and ‘feminisation’ of the breast

The medical definition of gynecomastia does not include pseudogynecomastia – as here the breast tissue may be of normal size. In many men, though, breasts are caused by some fatty tissue with some breast tissue.

Gynecomastia is much more common in overweight men as fat encourages the body to produce more estrogen. A doctor may be able to tell what is causing the swelling by examining the man, as breast tissue feels much firmer than fat. They may also ask for some scans to be sure if treatment such as surgery is necessary.

It is common to use gynecomastia or gyno to define or ‘def’ male breasts – whatever they are caused by.


Meaning of gyno

A man who is developing breasts may well wonder what is causing them, or what they mean. Gynecomastia can be caused by a variety of things. In most cases it does not mean anything sinister or worrying, and can often be fixed by some simple changes. Some of the causes of gyno are listed below:

  • Hormonal changes during puberty or in older age
  • Side-effects of prescribed medications
  • Recreational drugs – especially bodybuilding steroids or marijuana
  • Kidney or liver disease
  • Hormone secreting tumours
  • Rare genetic conditions

For a teenager, gynecomastia usually means nothing at all. He may be reassured by a visit to the doctor to check for any medical causes, but in most cases the breasts will go away on their own with a little time and patience.

Similarly for older men, there is often no sinister cause, and many men can be reassured and learn to live with some mild gynecomastia. In both cases, diet and exercise (where needed) can help reduce the breasts to a minimum.

For other men, breast tissue may mean they are experiencing a side-effect of some medication. Again, a visit to the doctor to discuss their medical conditions and whether a change in treatment might help is often all that is required.

For men who are taking bodybuilding steroids, the breasts mean that their body is reacting to the steroids by producing more estrogen. This is very common and men should be advised to stop using the steroids.

In all cases, consulting with a doctor will rule out any medical reasons for the gynecomastia, and the doctor can suggest how best to try and get rid of the problem.


So, what does gyno mean? In simple terms the word describes breasts which develop in a man. For many men these are not a serious condition and the problem can be fixed relatively easily with time, diet and exercise or a change in medication.

In rarer cases, gynecomastia can be a sign of something more worrying and could mean there is a problem in another organ or possibly even a tumour producing hormones. In all cases, if a man is worried he should discuss his gynecomastia with a doctor who should be able to help him understand what his gyno means.

Gynecomastia is defined as male breast development and the condition is often not worrying but serious medical causes need to be ruled out.

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