Stretch marks — those pesky lines on your belly, thighs and elsewhere — are most often caused by weight gain and pregnancy, which cause the skin fibers to stretch. An increase in the hormone cortisol, which causes the skin to lose elasticity, may also be to blame.

While stretch marks are often associated with pregnancy or gaining weight too rapidly, they can also occur if you build muscle too quickly. Bulking up too fast can make your skin stretch beyond its capacity and lead to stretch marks. Common areas for this to happen when working out are the arms, thighs, back and chest.

Stretch marks, also called striae, look like pink, purple or white streaks that spread across your skin. They occur because your skin stretches too quickly, such as during pregnancy or weight gain. Many treatments claim to reduce or eliminate stretch marks, but the truth is, there's no sure-fire cure for stretch marks.

Almost any department store has at least one cream claiming to fade stretch marks. Many of these products contain shea butter or cocoa butter as an active ingredient. Both are considered emollients, which help to moisturize the skin by replacing lost fatty acids.

Just like a rubber band, your skin is designed to stretch and snap back — when the skin stretches too far, it breaks instead of snapping back. This results in scar tissue development known as stretch marks. These red-and purple-markings can be the unsightly reminder of weight gain and/or a growth spurt.

Stretch marks appear virtually all over the body, with most instances on the back of the knees, thighs, stomach and arms. This is caused by rapid expansion of the skin, harming the natural elasticity that keeps the skin youthful looking.

Stretch marks are a common result of rapid growth in the body. The dermis layer of the skin helps to keep your skin elastic, but as the skin stretches, the dermis layer may be damaged and collagen deposits break down. Stretch marks are common in the hips, underarms, breasts and thighs.

Mederma produces a line of over-the-counter botanical creams and gels to help reduce the appearance of scars and stretch marks.

According to herbs2000.com, stretch marks are developed when the body is stretched beyond its elastic capacities. Intense weight training and dramatic weight gain are often ways unsightly stretch marks are created. Although they affect both genders, females are more susceptible to stretch marks than males.

Creams for old stretch marks are designed to help mask and even remove stretch marks that make your skin look old and deformed. While old stretch marks can also be removed with laser surgery, stretch mark creams are a cost effective way to look younger and keep your skin uniform and tight.

Stretch marks are a type of scar that occurs when the skin tears. They occur most often when you gain weight quickly and they are especially common during pregnancy. Stretch marks typically fade over time but generally don’t disappear completely.

Stretch marks are scars that can appear anywhere on the body that fat is stored, such as in the stomach, upper arms, thighs, breasts and buttocks. Body building, intense physical activity, childbirth and rapid weight loss are all causes of stretch marks.