Stretch Marks can be very annoying and bother many people. Mostly stretch Marks occur during pregnancy, but can also be seen during growth spurts or when they're a lot of weight gain. Stretch marks are a type of scar because of undue stretching of the skin, which is beyond its elastic limit. The skin fibres tend to break, and that leads to the appearance of stretch marks. These are scars that are there on the skin. They can appear on the abdomen, on the breast, on the thighs and even behind your knees.