Definition of Allergen
An allergen is any substance (antigen), most often eaten or inhaled, that is recognized by the immune system and causes an allergic reaction.
No comprehensive list of allergens is currently possible. Sensitivities vary from one person to another and it is possible to be allergic to an extraordinary range of substances.
Dust, pollen and pet dander are all common allergens, but it is possible to be allergic to anything from chlorine to perfume. Food allergies are not as common as food sensitivity, but some foods such as peanuts (really a legume), nuts, seafood and shellfish are the cause of serious allergies in many people. A few people have even been recorded to be allergic to certain chemicals found in almost all water. Poison ivy (and other plants, like poison sumac or poison oak) is a plant that will cause an allergic reaction for anyone, given enough repeated contact -- like any allergy, the human body must learn to fight the allergen, some bodies learn slower and will appear to be "immune" to poison ivy.
An allergic reaction can be caused by any form of direct contact with the allergen - eating or drinking a food you are sensitive to (ingestion), breathing in pollen, perfume or pet dander (inhalation), or brushing your body against an allergy-causing plant (direct contact, generally resulting in hives). Other common causes of serious allergy are wasp, fire ant and bee stings, penicillin, and latex. An extremely serious form of an allergic reaction, which can kill in mere minutes, is called anaphylaxis.
In addition to foreign proteins found in foreign serum (from blood transfusions) and vaccines, common allergens include:
- Airborne particles (hay fever)
- timothy grass
- birch trees
- Mold spores
- salicylates (also found naturally in numerous fruits)
- local anaesthetics
- Foods (food allergy)
- egg (typically albumen, the white)
- peas, beans, peanuts, soybeans and other legumes
- corn or maize
- Insect stings
- bee sting venom
- wasp sting venom
- Animal products (animal allergy)
- Animal hair and dander
- cockroach calyx
- dust mite excretion