An allergen is a substance that triggers an allergic reaction in people who are sensitive to that substance.
Each person may have their own unique set of allergens, and unique symptoms for each allergy. It is often very difficult to realize if someone has allergies or not. Because symptoms vary, it is impossible to know what allergen is the problem based on the reaction.
Common allergens include:
- Pet dander
- Sent (especially artificially scented perfume – horrible stuff)
- Insect stings
… to name just a few.