They can, but how you do it depends on the material. Traditional jute and burlap ghillie suits can mostly be machine washed on a gentle setting and left to air-dry. Manufacturers do not recommend this approach for polyester suits because the machine will likely damage the suit. Hand-washing in warm, soapy water is suggested. It’s a bit laborious, but it should stop all kinds of bugs and beasties taking up residence between hunting seasons.