Most allergens are proteins or glycoproteins that range in molecular weight from 5000 to 100,000 Da, although polysaccharides and low molecular weight substances also may be allergenic. Common allergens include pollens, fungal spores, house-dust mites, and animal epithelial materials but can also include drugs, biological products, and insect venoms. The allergic response is dependent on the route of exposure. If exposure is to an inhaled aeroallergen, the allergic response will be a respiratory reaction in nature. Ingested or injected exposure gives rise to gastrointestinal, cutaneous, or anaphylactic reactions. Size of pollen determines clinical manifestation of allergy. For example, particles between 20 and 60 μm in diameter can be carried in the wind and cause nasal and ocular symptoms (allergic rhinoconjunctivitis). Particles <7 μm can deposit in the airways and cause symptoms of asthma. Animals produce allergens in forms unique to each species. Cat allergen, most importantly Fel d 1, is found mainly in cat saliva, sebaceous glands in the skin, and in urine of male cats. It is buoyant and "sticky," which means it easily remains airborne and may last in a home for up to 6-9 months after the source is removed. Cat allergen adheres to clothes and can be found in public places such as schools. Dog allergen, particularly Can f 1, is present in dander, saliva, urine, and serum. There are allergens specific to dog breeds, but all breeds produce allergenic proteins (even poodles and "hairless" dogs).