Q: Why is it that a woman will get stretch marks as her belly grows during pregnancy, but children don't get them with all the growing they do? A: Actually, children undergoing a growth spurt can get stretch marks, or "striae". When skin is stretched at a rate faster than it can generate new skin, a stretch mark will appear. Continual stretching causes damage to the collagen and elastin fibers. Stretch marks are scars of the dermal (middle) skin layer with thinning of the epidermal (outer) skin layer. It's the thinning of the epidermis skin layer that causes a mature stretch mark to appear depressed and lighter in color than the rest of the skin. While 90 percent of pregnant women will develop some degree of striae, 70 percent of adolescent females and 40 percent of adolescent males (many of whom participate in weightlifting and contact sports) also get them to some degree. Because steroids (topical and oral) can cause thinning of the skin, they too are a potential cause of striae when used for extended periods. Genetic factors also play a part in one's risk of developing striae. Striae affect persons of all races, and are much more common in women. Q: What exactly is an "Achilles heel"? What causes it and what can be done to relieve the pain? A: Metaphorically and literally speaking, your Achilles heel isn't likely to disappear on its own. If you're wondering where the term comes from, its origin is in Greek mythology. Legend has it that baby Achilles was dipped in the river Styx by his mother Thetis to make him immortal. As Thetis immersed him, she held him by one heel but forgot to dip it in the river. The place where she held him remained untouched by the magic water and was thus mortal and vulnerable. Many years later, legend has it that he died as a result of an arrow wound to the heel. What we're describing anatomically is the strong tendon that connects the calf muscles to the heel bone. I can't tell whether you have tendonitis (inflammation of the tendon) or a tendon tear. Tendonitis is typically from an overuse injury like too much walking, tennis or jogging. A person with a low arch (flat foot) is more vulnerable to Achilles heel pain. So too is a woman who wears high-heeled shoes. Tendonitis is typically treated in the acute setting with the "RICE" protocol: Rest, Ice, Compression (support bandage) and Elevation of the leg. Anti-inflammatory medications like Ibuprofen or Aleve are also helpful. I'd recommend that you see an orthopedist or a podiatrist. Dr. Mitchell Hecht specializes in internal medicine. Send questions to him at: "Ask Dr. H," P.O. Box 767787, Atlanta, Ga. 30076. —P.J., Philadelphia —S.A., Tacoma, Wash.