An allergen is any substance that is recognized by the immune systems and is the cause of an allergic reaction. The substance most often is eaten or inhaled; some are even those caused by a scratch on the skin. Dust, pollen, and pet dander are all common allergens. Food like nuts, sea food, milk products, and fermented foods can be the cause of allergy symptoms in many people.

Giving a comprehensive list of allergens would be impossible. Neither would giving a common list be prudent because allergies are specific to persons. One person may exhibit a skin allergy where as another cat allergy. Some allergies are well known where as others are not. Perfume allergy and deodorant allergies are not so common.

Causative Factors

Common allergic reactions are due to the following causative factors. This list is not comprehensive and is based on statistical data of most occurring allergens. Airborne particles that cause hay fever are grass, weeds, birch trees, pollen, mold spores. Similarly a common list of food items that cause allergy are nuts, sesame, eggs, legumes(peas, beans, soybeans etc