Stretch marks are narrow, streak-like lines that can develop on the surface of the skin. They are also sometimes known as stria or striae.

Stretch marks are often red or purple at first, before gradually fading to a silvery-white colour. They are usually 1-10mm wide and are a few centimetres long.

The structure of the skin

The skin is made up of three main layers:

• The epidermis is the outer layer of skin. It forms a protective barrier for the inside of the body and is made up of layers of flat cells. 
• The dermis is the strong, supportive middle layer of skin that gives the skin its firmness and flexibility.
• The subcutis, also sometimes known as the hypodermis, is the inner layer of skin that consists of fat and connective tissue.

Stretch marks occur in the middle layer of skin (the dermis) when the skin is stretched considerably over a short period of time. The rapid stretching causes the dermis to break in places and allow the deeper layers of the skin to show through, forming stretch marks.

How common are stretch marks?

Stretch marks are very common. Anyone can get them, but they occur more often in women than men. The abdomen (tummy), buttocks and thighs are most commonly affected by stretch marks.

Stretch marks can appear on the skin whenever the skin is stretched as a result of sudden growth. For example, they can appear:

• during pregnancy
• as a result of weight gain
• as a results of growth spurts during puberty, when the body matures sexually and the reproductive organs become functional

About 9 out of 10 women are affected by stretch marks during pregnancy. Around 7 out of 10 females and 4 out of 10 males develop stretch marks during puberty.

In some cases, stretch marks can also be a symptom of an underlying health condition, such as Cushing's syndrome.

See Stretch marks - causes for more information about this condition.

Outlook

Stretch marks are not harmful. They do not cause any significant medical problems and there is no specific medical treatment for them. As a result, there is usually no need to see your GP about them.

Over time, the skin will contract (shrink) and the stretch marks will turn into white-coloured scars that are lighter in colour and less obvious. However, they do not usually fade completely.

Some people who have stretch marks find them distressing. If you are concerned or distressed about your stretch marks, discuss possible treatment options with your GP, such as laser therapy or cosmetic surgery.

However, there is no guarantee that these treatments will work for you and there is a lack of evidence that they are effective in treating stretch marks. See Stretch marks - treatment for more information.

Although there is no way to cure stretch marks completely, you can do a number of things to reduce your risk of developing them, such as looking after your skin and controlling your weight. See Stretch marks - prevention for more information and advice.

Abdomen

The abdomen is the part of the body between the chest and the hips.

High blood pressure

Hypertension is when the pressure of the blood in your bloodstream is regularly above 140/90 mmHG.

Tissue

Body tissue is made up of groups of cells that perform a specific job, such as protecting the body against infection, producing movement or storing fat.