Allergies are a common condition involving an abnormal response of the immune system triggered by a typically harmless substance. This substance (such as pollen, mold or animal dander) is known as an allergen. When a person is exposed to an allergen, their body produces antibodies and releases a variety of chemicals, including histamine. Histamine is the main cause of most allergy symptoms.
Allergic reactions usually result in mild symptoms such as:
- Runny nose
- Watery eyes
Moderate or severe reactions, called anaphylaxis, are rare but can be life-threatening and cause:
- Abdominal pain
For some patients, allergies can be seasonal and only cause reactions during certain times of the year. This condition is known as allergic rhinitis or hay fever and is usually caused by pollen and other allergens that are in the air from March until November.