Stretch marks seem to be caused, literally, by a stretching of the skin. Stretch marks are more extreme when coupled with an increase in cortisone, a hormone produced by the adrenal glands. Cortisone weakens elastic fibers in the skin. Stretch marks sometimes occur during substantial weight gain. Weightlifters can develop stretch marks, particularly on the arms. Adolescents may notice stretch marks during growth spurts. Stretch marks usually fade and become less noticeable over time and don't require any specific self-care or home therapy....