This article explains the basics of an allergic reaction. Learn what happens when your immune system goes on high alert.

Anyone can get them, at any age. You could develop them as a child, or you might not have any symptoms until you’re an adult.

While your problem may seem to start in the nose or the eyes, allergies actually come from an immune system run wild.

Asthma attacks (worsening of asthma symptoms) can be triggered by allergies, which can temporarily increase the inflammation of the airways in a susceptible person.

Sinusitis is an inflammation or swelling of the tissue lining the sinuses. Allergies can trigger sinusitis. 

Sometimes, allergies can cause a life-threatening reaction called anaphylaxis. It's not common, but you should be aware of what to do if it happens.

Nasal polyps are noncancerous, teardrop-shaped growths that form in the nose or sinuses. They’re often linked to allergies or asthma.