While your PJs may look and smell clean, sweat, dead skin cells, and bacteria can invisibly build up and contribute to acne and other skin conditions. How often your clothes need laundering depends on the materials you're wearing, how much you sweat, and even if you take a shower before bed—which can give you an extra day or two of wiggle room. While some people prefer to rotate their sleepwear on a nightly basis, the American Cleaning Institute suggests washing your pajamas after three or four wears.