An overview of allergens

Most allergens are proteins or glycoproteins that range in molecular weight from 5000 to 100,000 Da, although polysaccharides and low-molecular-weight substances may also be allergenic. Common allergens include pollens, fungal spores, house-dust mites, and animal epithelial materials but can also include drugs, biologic products, and insect venoms. The allergic response is dependent on the route of exposure. If the exposure is to an inhaled aeroallergen, then the allergic response will be respiratory in nature. Ingested or injected exposure gives rise to gastrointestinal, cutaneous, or anaphylactic reactions. The size of the pollen determines the clinical manifestation of allergy. For example, particles between 20 and 60 μm in diameter can be carried by the wind and cause nasal and ocular symptoms (allergic rhinoconjunctivitis). Particles of <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 buoyant and “sticky,” which means it easily remains airborne and may last in a home for up to 6 to 9 months after the source is removed. Cat allergen adheres to clothes and can be found in public places, e.g., schools. Dog allergen, particularly Can f 1, is present in dander, saliva, urine, and serum. All dog breeds produce allergenic proteins (even poodles and “hairless” dogs).