If shaving is irritating, it may be because it's time to replace your disposable razor. A Gillette study found that the average woman changes her blade less than once a month, but dermatologists advise tossing it after a few uses. A dull blade makes nicks more likely, and, if you've left the razor on the edge of a damp bathtub, it has probably been exposed to bacteria. "Shaving with a bacteria-ridden blade can cause folliculitis, the little red bumps that appear after a day or so," says Jeffrey Benabio, MD, a dermatologist for Kaiser Permanente in San Diego. So switch blades often, and store your razor in a clean, dry place.