Household dust. Coloured Scanning Electron Micro- graph (SEM) of a sample of household dust. Dust contains an assortment of substances which can cause an allergic reaction. The allergens here include textile fibres, hair, sand particles, skin scales, and remains from insects and dust mites. An allergy is a hypersensitive response to certain substances that, in most people, are harmless. Allergens may come into contact with the skin, respiratory airways, or surface of the eye. The substances seen here may also be found airborne in different quantities. Some allergens, for example pollen grains, occur in house dust seasonally. Magnification: x85 at 6x6cm size.