An allergy is a reaction to a substance called an allergen. Common allergens include:
- Wind-borne pollen (from grass, trees, ragweed)
- Mold
- Dust mites
- Furry and feathered animals
- Pests, such as cockroaches or rodents, in a home or other building
Normally allergens are harmless. But when a person has allergies, the body thinks these allergens are harmful. The body then attacks allergens with antibodies. Allergy antibodies are attached to special cells called mast cells. Allergens stick to the antibodies. This makes the mast cells release histamine and other chemicals. This is an allergic reaction. The chemicals irritate nearby nasal tissue. This causes nasal allergy symptoms. When this happens in the breathing tubes of the lungs, it can cause asthma symptoms, such as cough and wheeze.