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What Causes Stretch Marks?

Stretch marks, or striae, appear as indented lines or streaks in your skin when your skin “stretches” quickly during periods of rapid growth. They occur most often during pregnancy and periods of fast weight gain. While women are 2.5 times more likely to develop stretch marks, they can affect men, teenagers, and bodybuilders.

Stretch marks form in the middle layer of your skin when the fibers there undergo rapid growth or stretching. While your skin is fairly elastic, overstretching can disrupt the normal production of collagen and elastin in the inner layer of skin called the dermis. Small tears result from the stretching. 

Stretch marks first appear as raised or bumpy red, purple, or brown lines on the trunk, legs, arms, flanks, and breasts. Some people experience itching or soreness at the site of stretch marks. After these dermal fibers tear, they eventually heal into linear, indented stretch marks. They fade to smoother white or silver lines over time.

One of the most effective ways to improve the appearance of stretch marks involves laser treatment. Skin care specialist James Volpe, DO, of GLO Aesthetics in Philadelphia, has over 20 years of experience in primary care and aesthetics and is double-board certified in family medicine and hospice and palliative medicine by the American Osteopathic Board of Family Physicians. Dr. Volpe and his technicians provide expert treatment with the Icon™ Aesthetic System to help fade and often erase unattractive stretch marks so patients can return to smooth and firmer skin. 

Stretch marks tend to run in families so you may have a higher risk of developing them if you notice stretch marks on close family members. They are also associated with certain genetic conditions including Cushing’s syndrome and Marfan syndrome. Find out more about stretch marks and what causes these unwanted marks to appear.


Pregnancy is the most common cause of stretch marks, with between 50 and 90% of pregnant women developing stretch marks before their babies are born. Signs of stretch marks typically appear by the seventh month of pregnancy.

During pregnancy, the skin doesn’t have enough time to adjust as your body constantly stretches to accommodate a growing baby. Some experts believe that the hormonal changes in pregnancy attract more water into your skin, which causes your skin to relax and tear more easily when stretched.

Stretch marks occur when the skin tears as your body expands faster than the skin covering it. While stretch marks develop most often on your abdomen during pregnancy, they can occur on any part of your body where you gain weight. Gaining weight slowly and steadily during pregnancy may help prevent the development of stretch marks.


Rapid growth and weight gain can trigger the appearance of stretch marks in both girls and boys during puberty. Girls are more likely to develop stretch marks in areas of the body where fatty deposits occur and areas specifically designed to facilitate childbearing. Stretch marks typically appear on the sides or underneath girls’ breasts and hips as these areas grow quickly and the skin must stretch to cover the additional surface area. Stretch marks may also appear around the upper thigh and buttocks.

Boys develop stretch marks in different places. Working out during puberty can result in stretch marks along the shoulder line as boys’ bodies stretch to cover larger biceps. Stretch marks may also develop on thighs when a boy’s leg bones grow quickly to accommodate gains in height. Boys who don’t have a lot of baby fat may get stretch marks on their buttocks as additional fatty deposits develop in this area.

Rapid growth or weight gain

Periods of rapid growth or weight gain aren’t limited to pregnancy and puberty. Anyone who participates in weight training and bodybuilding can increase their risk of stretch marks by growing bigger muscles in a short period of time. However, the risk for developing stretch marks for men typically declines after age 40, when men lose their ability to add muscle mass at a rapid rate.

Having breast augmentation can increase the risk for stretch marks for women, especially if you’re susceptible to developing them. Getting larger implants also makes the development of stretch marks more likely.


Using oral or topical corticosteroids for too long can lead to adverse side effects including stretch marks. While these prescription medications can be effective for short-term treatment of conditions such as eczema, rheumatoid arthritis, and lupus, they can induce weight gain and thinning and stretching of the skin. Even over-the-counter hydrocortisone can thin your skin over time and increase your risk of developing stretch marks. 

Find out more about the causes of stretch marks and how you may be able to improve their appearance by calling or requesting an appointment online today.

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