Stretch marks - Causes of stretch marks

Stretch marks are the result of rapid stretching of the skin due to sudden growth or weight gain.

This stretching causes the middle layer of skin (the dermis) to tear, allowing the deeper skin layers to show through, forming stretch marks.

The dermis contains strong, inter-connected fibres that allow your skin to stretch as your body grows. However, rapid growth can over-stretch and break the fibres.

The tears in the dermis allow the blood vessels below to show through. This is why stretch marks are often red or purple when they first appear.

When the blood vessels eventually contract, the pale-coloured fat underneath your skin will be visible, and your stretch marks will change to a silvery-white colour.

When stretch marks occur

Stretch marks often occur:

• during pregnancy
• after rapid weight gain
• during puberty
• if you have a family history of stretch marks
• if you have an underlying health condition or a syndrome, such as Marfan syndrome
• after the prolonged or inappropriate use of corticosteroid medication  

These are discussed in more detail below.

Pregnancy

Stretch marks are common during the later stages of pregnancy, affecting about 8 out of 10 pregnant women. Whether or not you'll get stretch marks depends on your skin type and how elastic it is.

During pregnancy, your body produces hormones that soften the ligaments in your pelvis so they're more flexible when you give birth. Ligaments are strong bands of tissue that connect joints. However, the hormones also soften the fibres in your skin, making you prone to stretch marks.

As your baby grows, you may get stretch marks on your tummy, as your skin stretches. You may also develop stretch marks on your thighs and breasts as they get bigger.

After childbirth, stretch marks usually fade and become less noticeable, but they don't always disappear completely.

Rapid weight gain

You may get stretch marks if you put on a lot of weight over a short period of time.

The stretch marks sometimes remain even after losing weight, but should eventually fade.

If you diet regularly, stretch marks can occur as your weight goes up and down. Should you need to lose weight, lose it slowly and steadily so that your skin isn't put under strain.

Read more about how to lose weight safely.

Bodybuilders and athletes can also get stretch marks as their muscles increase in size.

Puberty

During puberty, the body often develops very quickly in growth spurts.

Boys may get stretch marks on their shoulders and back, and girls may get them on their hips, thighs and breasts.

Family history

If you have a close relative with stretch marks, such as your mother, you're more likely to develop them yourself.

Although stretch marks can affect both male and female members of your family, they're most common in women.

Underlying health conditions

Stretch marks can sometimes be caused by rare, underlying health conditions or syndromes, such as Cushing's syndrome and Marfan syndrome.

Cushing's syndrome occurs when the body overproduces the hormone cortisol, which is thought to cause stretch marks to develop.

Marfan syndrome is caused by a faulty gene that affects your body's skin and connective tissues. It weakens your body's tissues, reducing their elasticity (ability to stretch). This means your skin isn't as resistant to stretch marks as it should be.

If you have Marfan syndrome, you may develop stretch marks on your shoulders, hips or lower back.

Corticosteroids

In rare cases, stretch marks can develop after prolonged or inappropriate use of corticosteroid medicines, such as creams or lotions used to treat skin conditions, including eczema.

Corticosteroids work in a similar way to the hormone cortisol, which is naturally produced by your body.

Corticosteroids can help ease inflammatory skin conditions; however, like cortisol, they can also decrease the amount of collagen in your skin.

Collagen is a protein that helps to keep your skin stretchy. This means that the less collagen there is in your skin, the more likely you are to develop stretch marks.

When using a corticosteroid cream or lotion, make sure you follow the manufacturer's instructions about how and where to apply it. The face, groin and armpits are particularly sensitive areas. If you're unsure, ask your GP or pharmacist for advice.