If you have cellulite, stretch marks or both, you are not alone. A whopping 90 percent of women have cellulite and 80 percent of Americans have stretch marks. They are both harmless, but that probably doesn't make their appearance bother you any less.

Stretch marks from rapid weight gain or pregnancy can be embarrassing and unsightly. The red marks that occur when your skin stretches too fast may be dark or light, long or short, deep or shallow.

Exercise has a lot of benefits to your skin's health, but eliminating stretch marks is not one of them. Stretch marks are made up of scar tissue and can cover a large swath of skin. Many people develop these in regions where weight gain is common, such as the thighs, hips, buttocks, stomach and arms.

Stretch marks are called as such because they develop when your skin has stretched significantly in a short period of time. Common reasons for developing stretch marks are pregnancy, rapid weight gain and steroid usage.

Some people seem to get stretch marks at the slightest sign of weight gain, while others have resilient skin that resists all stretching.

Stretch marks are typically caused when the skin suddenly expands. Pregnancy and weight gain are common causes of developing stretch marks. This skin problem, however, can be frustrating and embarrassing.

Stretch marks may appear on a woman’s stomach when she becomes pregnant, because of the rapid stretching of skin from the baby growing and developing -- but stretch marks can occur on almost any part of your body.

Stretch marks are not simply caused by skin stretching from growth. They are triggered by hormonal changes in the body, according to The Patient’s Guide website. Often, stretch marks become inflamed, says the site, making them ripe for acne breakout, as well.

Stretch marks are mostly associated with abdominal and leg skin. However, stretch marks can also appear on a person's breasts. If you notice stretch marks on your breasts, there is no cause for alarm; this is actually fairly common.

A woman’s body goes through many challenges during pregnancy: sore breasts, hemorrhoids and, of course, stretch marks. When skin stretches beyond traditional boundaries, tears form in the derma and streaks appear across the surface. For many people, stretch marks are ugly, but not terribly painful.

Toning the muscles in your body is an effective method to improve your appearance. Doctors and other experienced professionals often recommend strength-training activities, such as weightlifting, to add muscle mass and to improve bone strength and balance that otherwise diminish as you age.

Stretch marks appear in a variety of colors and shapes. Some may be pink or red and leave indentations in the skin. Others may be just purplish streaks. Whatever the appearance, stretch marks can be concerning. Especially when the cause is not known.