According to WebMD, stretch marks are discolorations or scarring in the skin after it has been stretched out due to significant weight loss, weight gain or pregnancy. The marks form as a result of the middle layer of the skin being stretched out rapidly and not bouncing back to its original elasticity.
Stretch marks are often reddish or purplish in color and change to a fish scale appearance over time. They are commonly found on the hips, breasts, stomach, lower back and upper arms. There are several types of treatments available to remove them. The effectiveness of treatment can depend on age, diet and skin tone.