How often you should wash them: After two to five wears.
Washing guidelines: You should wash cotton, silk, and cashmere after two to three wears, since these pieces are more delicate. Wool and durable man-made blends, such as acrylic and polyester, can withstand five wears. “Wool naturally repels dirt, dust, and liquids,” says Sue Benfield, a sweater designer for Woolrich. Whatever the fiber, follow the care instructions on the label.
What else you should know: Hand washing tends to be gentlest, but if you’re worried about moths, take knits to the cleaners. “Once larvae have bored into the fabric, it may be too late to prevent holes,” says Steve Boorstein, the host of the DVD The Clothing Doctor’s Secrets to Taking Control! ($20, amazon.com).