The normal lifespan of a pillow is two to four years. Replacement is recommended for sanitary reasons. All types of pillow covers should be laundered periodically since they are the part that is in contact with a person's body. Pillows accumulate dust and microbes among the fill, even when washable pillows are washed. Manufacturers recommend tumble-drying for fifteen minutes every week to freshen them up, and for the heat to kill dust mites. Charities in most countries will not accept used pillows due to hygiene regulations. While some animal shelters accept forms of bedding, most reject donation of used pillows due to the mess they can cause.