Stretch marks happen. Whether from pregnancy, rapid weight gain or loss, weight lifting, or a growth spurt in your early teens, countless women and men experience the frustrating but common skin problem. Yes, even the stars get them. Leann Rimes recently tweeted about her stretch marks and how she’s had them for years, and pop diva Jennifer Lopez even showed off a pre-airbrushed image from a recent photo shoot that bared her stretch marks. But what exactly are stretch marks and how do they form on your skin? If you’re curious, we have the inside scoop.

So, What Causes It?

Stretch marks (or “striae”) are caused when extreme changes in the shape of your body result in tearing of the lower layers of your skin. Skin is composed of multiple layers. The topmost layer of your skin is called the epidermis. Beneath the epidermis is the layer of skin known as the dermis. It is in the dermis where stretch marks form. Because the tearing that creates stretch marks occurs in the dermis, it does not bleed or scab like an external would, but the damage is visible in the form of stretch marks. Over time, the tears heal and form scars. This is why stretch marks appear initially as some hue of red but will fade and become white over time.

So what does cause the unsightly red and purple marks? The true cause of stretch marks is hormones. During periods of growth — when women are pregnant, when people are lifting weights and gaining muscle mass, or when growth spurts happen during teen years, a serious change in hormones and a change in the metabolism in the skin occur. It’s true that your skin is expanding as your body is expanding, “but it’s the hormonal changes and not the ‘stretching’ that is the cause of stretch marks,” Dr. Bernstein explains.

Who is Most at Risk?

Although anyone can develop stretch marks at any point in their life (men and women), certain lifestyle events are more likely to result in developing them and are higher risk.  These are:

  • PregnancyMore than half of all women get stretch marks while pregnant, so your concerns are justified.
  • Weight lifting and body buildingBecause rapid muscle development can lead to stretch mark scarring, bodybuilders must take preventative measures to prevent skin from stretching and scarring
  • Dieting and Weight Gain/LossWhen the body expands rapidly due to weight gain, skin must stretch to compensate for the body’s growth
  • Puberty

Common Treatment Methods

Unlike invasive surgeries of the past like abdominoplasty, the typical methods of treatment don’t require surgery with all of the related costs and downtime for recovery.  The two most common methods are:

Stretch Marks: The Bottom Line

The bottom line is that anything that changes the hormones in your body and your skin — from pregnancy and birth control pills to rapid weight gain or loss and growth spurts — can all cause stretch marks.

Knowing what causes stretch marks won’t make them go away (unfortunately), but the more facts you have about what’s happening to your body, there easier it is to find ways to alleviate the problems you’re facing. If you’re dealing with stretch marks, talk to you doctor about the best options for minimizing them.