Overview
Allergies happen when the immune system reacts to a trigger that is usually harmless, such as pollen, pet dander, foods, insect stings, or some medicines. Reactions can be mild, but some can become serious very quickly.
How common is it?
Allergies are common and can affect people of any age. Some people have one type of allergy, while others react to several different triggers.
Causes and risk factors
Allergy symptoms happen when the immune system overreacts to an allergen. Common triggers include pollen, dust mites, mould, animal dander, foods, insect stings, and some medicines.
Common risk factors
- A family history of allergies, asthma, or eczema
- Asthma or eczema
- Regular exposure to pollen, dust, mould, or animals
- Food or medicine triggers
- Previous allergic reactions
Symptoms
- Sneezing or a blocked or runny nose
- Itchy, red, or watery eyes
- An itchy rash or hives
- Coughing, wheezing, or breathlessness
- Swelling of the lips, eyes, mouth, or throat
- Tummy pain, vomiting, or diarrhoea after some triggers
When to see a doctor
For sudden mouth, tongue or throat swelling, breathing difficulty, faintness, collapse or reduced responsiveness, use a prescribed adrenaline auto-injector immediately if available and call your local emergency number. Lie flat with legs raised; if breathing is difficult, raise the shoulders or sit up slowly. Do not stand or walk. In pregnancy, lie on the left side. Use the second injector after 5 minutes if not improving. Arrange a routine assessment for suspected allergy without emergency symptoms.
Diagnosis
A clinician usually diagnoses allergies by asking about symptoms, timing, and likely triggers. Skin prick tests or blood tests may help confirm the cause, especially if symptoms are severe, unclear, or affect foods, medicines, or insect stings.
Treatments
Avoiding the trigger
The safest long-term plan is to avoid the thing that causes symptoms when possible, such as a food, medicine, pollen, or pet exposure.
Medicines for symptom relief
Antihistamines, steroid nasal sprays, creams, or other treatments may help depending on the type of allergy and the symptoms you have.
Emergency treatment for severe reactions
People at risk of anaphylaxis may be prescribed two adrenaline auto-injectors and an emergency plan. Use adrenaline promptly for suspected anaphylaxis and call emergency services, even if symptoms improve. Antihistamines do not replace adrenaline for anaphylaxis.
Self-care and lifestyle
- Keep a note of likely triggers and symptoms
- Read food and medicine labels carefully if you have known allergies
- Carry two adrenaline auto-injectors at all times if prescribed, know how to use your particular device and check expiry dates
- Follow your allergy action plan and check expiry dates on emergency medicines
Prevention
You cannot always prevent allergies, but avoiding known triggers and having a clear plan can reduce the risk of severe reactions. Specialist treatment such as immunotherapy may help some people with selected allergies.
Sources and review
Last reviewed: 28 July 2026 by Living Diabetes Editorial Team. This guide was checked against current patient and professional guidance. It is educational and does not replace care from your own healthcare team.