Allergic reactions
You have had an allergic reaction which means that your body’s immune system has had a hypersensitive reaction (overreaction) to a harmless substance called the allergen.
What is an allergic reaction?
An allergic reaction can present with one symptom or a combination of symptoms.
- Urticaria (hives) are common—they are itchy, red eruptions on the skin which can be localised or become widespread and flow together
- Lip, tongue and throat swelling which can cause hoarseness and itchiness
- Allergic conjunctivitis with itchy, watery red eyes
- Allergic rhinitis with a stuffy or runny nose and sneezing
- Wheeze and shortness of breath or developing a cough
- Nausea and vomiting with abdominal pain and diarrhoea
- Anaphylaxis is a severe allergic reaction that is rapid in onset and is potentially life-threatening—it can cause breathing difficulties and low blood pressure and is a medical emergency
What can you be allergic to?
Almost anything can trigger an allergic reaction if you are susceptible. Common allergens are:
- Foods such as nuts, dairy products, shellfish, fruits and grains—it is not the same as food intolerance when your body is unable to breakdown that particular food
- Dust and pollen
- Medication such as antibiotics (eg penicillin)
- Latex or rubber
- Chemicals in detergents, hair dyes or tattoos
- Insect bites
Often no obvious cause can be found unless it has occurred frequently to the same allergen.
Who gets allergies?
You may be more at risk of sustaining an allergic reaction if you:
- Have a family history of an allergy
- Have other allergies (several allergens are linked to one another)
- Have a history of asthma, hayfever, eczema or other atopic disorders
What should you do if you have an allergic reaction?
Anaphylaxis and severe reactions
You should seek urgent medical advice as soon as possible especially if:
- It is a rapidly developing reaction
- You feel unwell and feel faint
- Your mouth, throat or lungs are affected and you have problems breathing or talking
- You have had previous severe reactions
Always call 999 if concerned. You may need adrenaline into your muscle.
Mild or moderate allergic reaction
Symptoms that are minor, less severe or developing over longer periods of time can be treated with:
- Oral antihistamines (eg chlorpheniramine) which help with symptoms—there are many others available over the counter including once daily non-sedating drugs (eg cetirizine, loratadine)
- Steroids—you may be given a short course of oral corticosteroids (eg prednisolone for three days) if it is a severe reaction (other preparations available over the counter include steroid creams for rashes or insect bites, or nasal sprays for rhinitis—discuss with your pharmacist or GP)
- AVOID known allergens or triggers
Do you need hospital admission or investigations?
Most people with allergic reactions can go home and require no emergency blood tests. It is a clinical diagnosis.
If you have a severe allergic reaction, anaphylaxis or require adrenaline then you will be admitted for monitoring and may require blood tests.
How quickly will it get better and will it happen again?
Acute response
- Most people see a rapid improvement (in less than one hour) with treatment
- After an acute reaction there is a rare risk of it coming back within a few hours if the medication wears off or you are still exposed to the allergen so you need to be vigilant
- Sometimes the allergic rash can take several days to weeks to disappear—if you are well with no other symptoms then do not worry and see your GP
Recurrence of allergic reaction
- Avoid any known allergen to prevent future reactions
- If you are having recurrent allergic reactions to an unknown cause then your GP can refer you to an allergy specialist (immunologist) for further investigations.
Further information
Further information is available at: