Allergic reactions A&E leaflet

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What is an allergic reaction?

An allergic reaction happens when your immune system overreacts to a harmless substance (allergen). Reactions can range from a mild rash to serious breathing or blood pressure problems. 

The most severe reaction is anaphylaxis (anaphylactic shock). This is a life-threatening emergency that needs urgent medical treatment. 

Most allergic reactions happen soon after contact with an allergen. However, there can be delayed in symptoms. In some cases, symptoms may return within six hours, particularly if adrenaline was needed. 

What are common allergens?

A variety of substances can cause an allergic reaction.

Food

Often caused by proteins in foods like nuts (especially peanuts), fish, shellfish, eggs, and cow’s milk. symptoms usually start right after eating but can sometimes take hours. Food allergies are more common in people with asthma, eczema, or hay fever. 

Insect stings

Usually from wasps or bees, with reactions occurring within 30 minutes. 

Latex (natural rubber)

Found in some condoms, balloons, gloves, rubber bands, carpet backing, and medical supplies. 

Medicines

Reactions often occur after taking a medicine for the first time, and they happen faster if the medicine is injected directly into a vein. 

Unknown causes

Sometimes, especially in adults, no clear cause is found. 

How to avoid allergens?

The best way to prevent an allergic reaction is to avoid the allergen.

Food allergies

• Avoid even small amounts of the food unless advised otherwise by an allergy specialist. 
• Check food labels carefully. When eating out, ask about ingredients and explain your allergy. If they can not guarantee safety, eat elsewhere. 
• Be cautious when preparing food to prevent cross-contamination. 

Insect stings

• Wear neutral-coloured clothing and closed shoes in warm months. 
• Avoid perfumes and sweet-smelling products. 
• Keep food covered outdoors, avoid open bins, and remove fallen fruit. 
• Keep windows closed and use fly screens or insect repellent. 
• Remove wasp or bee nests quickly. 

Latex

• Tell healthcare providers and hairdressers about your allergy. 
• Latex exposure is riskier during medical procedures, so warn staff beforehand.

Medicines

• Learn the exact name of any medicine you are allergic to (not just brand names). 
• Always inform healthcare professionals about your allergies. 

What are the symptoms of an allergic reaction?

The following symptoms may occur:

Mild to moderate symptoms

• Feeling hot or cold, anxious, or flushed. 
• Tingling, itching, or burning sensations, or a strange taste in your mouth. 
• Itchy skin, throat, or eyes. 
• Swelling of the face or lips. 
• A rapidly developing rash (hives or wheals). 
• Abdominal pain, nausea, or vomiting. 
• Mild wheezing. 

Severe symptoms (anaphylaxis)

Anaphylaxis is a severe allergic reaction requiring urgent treatment with adrenaline (epinephrine). Symptoms include: 

• Severe swelling of the tongue or throat causing difficulty breathing. 

• Difficulty talking or a hoarse voice. 

• Severe wheezing or difficulty breathing. 

• Feeling pale, clammy, faint or dizzy. 

• Confusion, disorientation, or unresponsiveness. 

How to treat an allergic reaction?

Always be prepared

• Keep antihistamines on hand, along with a blue reliever inhaler (for example, salbutamol) if prescribed. 
• If you have an adrenaline pen prescribed, ensure it is within its expiry date. 
• Make sure you and those close to you are trained in using an adrenaline pen. Training videos and practice devices are available on manufacturers’ websites. 
• Consider wearing a medical alert bracelet to inform others of your allergy. 

Mild to moderate reactions

• Take an antihistamine immediately. 
• Use a reliever inhaler if you have mild wheezing. 
• Have someone monitor your symptoms. If reaction does not improve or gets worse seek medical attention.   

Further information

Anaphylaxis UK

Allergy UK

Asthma UK

Epipen UK

Jext

For general medical advice please use the NHS website, the NHS 111 service, walk-in-centres, or your GP.
NHS website provides online health information and guidance.
There are walk-in and urgent treatment services at Brighton Station, Crawley Urgent Treatment Centre, Lewes Victoria Hospital, Horsham Minor Injuries Unit and Bognor Regis War Memorial Hospital.