on allergic reactions, asthma and can irritate skin conditions such as eczema. A full zippered encasement allergen filtration mattress protector can provide an extra layer of protection between the user and their mattress, filtering allergens that are known to trigger allergy and asthma symptoms. For protection against bed bugs, the mattress and box spring must both be fully enclosed with no possible openings. Zippered cases are commonly used for this purpose. This prevents new bed bugs from getting into the mattress and box spring, and traps any bed bugs that are already inside. Mattress protectors must be left on for at least a full year to make sure that the trapped bed bugs and their eggs die. If the cover is taken off early, the bed bug infestation may relapse. Waterproof mattress protectors also reduce allergy symptoms by reducing the ability of mold to grow in a mattress. Mattress protectors which can be easily disinfected are commonly used in children's nurseries and health care facilities. A 2002 Norwegian study has found that foam mattresses are 4 to 8 times more likely to host dust mite feces than spring mattresses. Types There are different types of mattress protectors. Encasements are shields that protect the mattress directly, typically from bed bugs, and are often used in hotels. Protectors are used to protect the mattress from bed-wetting or allergic situations. In contrast, mattress pads and mattress toppers are primarily used to provide comfort features for the user. Pads are thinner, while the thicker toppers tend to be more comfortable and expensive. One type of mattress topper is a featherbed, made either with feathers, down, or a combination of both materials; featherbeds may need to be frequently shaken out or fluffed, to keep the feathers evenly distributed. Disposable underpads In hospital or other medical settings, a disposable underpad may be used to absorb blood and other bodily fluid, in concert with a hospital gown. This is sometimes light blue and known as chux pad, after an old brand name for a disposable diaper. See also Futon (of similar dimensions to a mattress topper) Bed base References Mattresses Bedding Bed bug