“Bra Whisperer" Susan Nethero told the Orange County Register’s "Style Binge" column that bras can be worn twice before they need to be washed. But avoid wearing the same bra two days in a row. That will give the elastic time to bounce back and offer your “girls“ better support. In a separate interview with "Woman's Day" magazine, Nethero recommended using a netted laundry bag for machine washing and cautions against putting your bras in the dryer.
Unless you exercise a lot or sweat heavily, you can probably get away with washing your bra after wearing it twice. Use a gentle detergent to hand-wash your bras, or machine wash in cool water on the delicate cycle and let them air dry.