The term stretch mark refers to streaks and lines that appear due to major stretching or expansion of the skin in a particular area. Studies have revealed that stretch marks are a weakening of all the key fibers of the skin including collagen, elastin and other connective tissue components. This condition is most commonly associated with an elevated level of hormones. During pregnancy women may experience the onset of stretch marks on the abdomen, thighs, and hips. Men who participate in a vigorous weight lifting program with associated muscle increases often develop stretch marks across the shoulders or other areas of muscle development associated with this activity. Even young people going through growth spurts at puberty may experience stretch marks.