An allergy happens when the immune system reacts to something that's normally harmless, such as pollen, dust mites, pet dander, certain foods or insect stings. Common symptoms include sneezing, itching, a runny nose, a rash, or in more serious cases, swelling and difficulty breathing.
Most mild allergies can be managed with over-the-counter antihistamines and by avoiding known triggers where possible. However, severe allergic reactions (anaphylaxis) are a medical emergency and need immediate treatment. If you suspect you have an allergy, particularly to food or medication, it's worth getting it properly diagnosed by your GP or an allergy specialist rather than guessing at the cause.
See also our page on hay fever, one of the most common seasonal allergies.
Common questions
What is an allergy?
An allergy happens when the immune system reacts to something normally harmless, such as pollen, dust mites, pet dander or certain foods.
When is an allergic reaction a medical emergency?
A severe reaction (anaphylaxis) needs immediate treatment. Mild allergies can usually be managed with antihistamines and by avoiding known triggers.