Symptoms of an allergic reaction usually develop within a few minutes of being exposed to something you're allergic to, although occasionally they can develop gradually over a few hours.
An allergy is a reaction your body has to a particular food or substance. Allergies are particularly common in children, but adults can get them too.
Allergy symptoms include sneezing, wheezing and itchy eyes. A life-threatening allergic reaction can also cause swelling and breathing difficulties.
If you have an allergy, try to avoid the thing you're allergic to if you can. Medicines like antihistamines can help ease symptoms if you need them.
Allergies are caused by your immune system mistaking a harmless substance for something harmful. Common triggers include pollen, food and animals.
Page last reviewed: 22/11/2018
Next review due: 22/11/2021