Allergies are caused by an over-sensitive immune response. The immune system normally protects the body against harmful substances such as bacteria and viruses. Allergy symptoms occurs when the immune system reacts to substances (allergens) that are generally harmless and in most people do not cause an immune response. When a person with allergies breathes in an allergen such as pollen or dust, antibodies are produced. When the antibodies are stimulated by pollen and dust, histamine and other chemicals are released. This causes itching, swelling, and mucus production. Symptoms vary from person to person. Very sensitive individuals can experience hives or other rashes. Hay fever involves an allergic reaction to pollen. A similar reaction occurs with allergy to mold, animal dander, dust, and similar inhaled allergens. The pollens that cause hay fever vary from person to person and from region to region. Large, visible pollens are seldom responsible for hay fever. Tiny, hard to see pollens more often cause hay fever. Examples of plants commonly responsible for hay fever include: - Trees (deciduous and evergreen)
- Grasses
- Ragweed
The amount of pollen in the air can play a role in whether hay fever symptoms develop. Hot, dry, windy days are more likely to have increased amounts of pollen in the air than cool, damp, rainy days when most pollen is washed to the ground. Some disorders may be associated with allergies. These include eczema and asthma. Allergies are common. Your genes and environmental may make you more prone to allergies. | 
Allergy & Immunology
