Red flag: Large, dusky blue leg veins

What it means: Some of your veins are no longer working properly when you spy ropy, blue-to-purple lines snaking up your legs. Venous disease -- a.k.a. varicose veins -- can be a mere cosmetic annoyance or can cause pain, cramping, and difficulty walking. Veins rely on one-way valves, like shutters, to keep blood circulating; when they stop working, blood leaks back into the vein and pools there.

More clues: Varicose veins are sometimes mistaken for spider veins, a weblike network of smaller blue or red veins closer to the skin's surface. Varicose veins tend to be larger, darker, and sometimes raised, with a twisted appearance. (The name comes from the Latin varix, or "twisted.") Half of all people over age 50 have varicose veins, especially women. They often first appear in pregnancy.

What to do: Exercise, compression stockings, and avoiding constricting postures (like crossing your legs when seated) can help ease discomfort, but they won't make varicose veins disappear. Not all faulty veins cause problems. However, if the veins cause pain or become warm and tender to the touch, tell your doctor. Severe venous insufficiency can lead to dangerous blood clots. Treatments with good success rates include sclerotherapy (injecting a solution to shut the vein) and surgery -- also options if you just can't bear how your legs look at the beach.