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Allergic reactions ED

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What is an allergic reaction?

  • An allergic reaction occurs when the body’s immune system reacts to a normally harmless substance, an ‘allergen’. This can cause a wide range of symptoms from a simple rash to problems with blood pressure or breathing.
  • Anaphylaxis or anaphylactic shock is the most severe type of allergic reaction. The body over-reacts to the allergen and a severe allergic reaction occurs needing immediate medical attention to avoid potentially fatal results.
  • Most reactions occur quickly after ingestion or contact with the allergen. Rarely, they occur after a few hours. Symptoms can recur usually within six hours of the first reaction in some patients particularly if they have needed adrenaline.


    A variety of substances can cause an allergic reaction.


    Often caused by the protein component. Common allergens are nuts (especially peanuts), fish, shellfish, eggs and cow’s milk. Most reactions occur immediately after swallowing. Rarely, they may begin several hours after eating. Food allergies are more common in those with other allergic conditions such as asthma, eczema and hayfever.

    Insect stings

    Especially wasp and bee stings. The reaction is usually immediate (within 30 minutes).

    Natural rubber/ latex

    This can be found in some contraceptives (condoms, diaphragms), balloons, rubber gloves, rubber bands, carpet backing, furniture filling and medical items such as catheters, gloves and some disposal items.


    Reactions usually occur after the first course and occur more quickly if the medicine is given by a line straight into a blood vessel.

    Idiopathic/ unknown

    Occasionally, especially in adults, a cause cannot be identified.

    Avoiding allergens

    You will not experience an allergic reaction if you can avoid the allergen.


    • Avoid eating even a small amount of a food that you are allergic to (unless advised differently by the allergy clinic). Skin contact may also cause a reaction.
    • Read labels carefully. Ask about ingredients that you are allergic to, when eating in food outlets. Stress the seriousness of your allergy and eat elsewhere if the outlet cannot guarantee that the food item is safe.
    • Dieticians and food manufacturing companies can also provide advice.
    • Take extra care when preparing food to avoid cross-contamination.

    Insect stings.

    Avoid bright clothing in warmer months. Wear shoes when outside. Avoid perfumes and fragrances. Avoid eating and drinking sweet foods outside. Avoid open bins, keep food covered and avoid picking fallen fruit. Keep windows closed. Use fly nets and insect repellants. Ensure nests are removed promptly.


    Warn healthcare staff and hairdressers of your allergy. Latex contact with mucous membranes or body tissue (e.g. during surgery) is more likely to cause a severe allergic reaction.


    Ensure you know the proper names of any medicines you are allergic to (not just the brand names). Ensure healthcare staff are aware of any allergies you have.

    Signs and symptoms

    The following symptoms may occur

    Mild/ moderate.

    • Feeling hot/ cold, anxious, flushed.
    • Tingling, itching or burning feeling or nasty taste in your mouth.
    • Itchy skin, throat, eyes.
    • Swollen face or lips.
    • Quickly developing rash (wheals/ hives).
    • Abdominal pain, nausea, vomiting.
    • Mild wheeze.

    Severe (anaphylaxis).

    Any of the following needs urgent treatment with adrenaline (epinephrine)

    • Severe swelling of the tongue or throat with difficulty in breathing.
    • Difficulty talking or hoarse voice.
    • Severe wheeze or breathing difficulty.
    • Feeling pale, clammy, faint or dizzy.
    • Becoming disorientated or unresponsive.

    Managing an allergic reaction

    • Always have antihistamines, and if prescribed, a blue (salbutamol/ reliever) inhaler or adrenaline pen available.
    • If you have an adrenaline pen, ensure it is in date and that you and your close family/ friends are trained in its use (see manufacturer websites for training videos and devices). Consider wearing an alert bracelet about your allergy.
    • Mild/ moderate symptoms. Take an antihistamine. Treat mild wheeze with a reliever inhaler. Ask someone to monitor you to ensure you are not getting worse.
    • Severe symptoms. Use your adrenaline pen if you have one. Call 999 and state that you are having a severe allergic reaction.
    • Lie down if you feel faint. Sit up if you feel breathless.
    • A second adrenaline pen can be used if there is no improvement after 10 minutes. Note the time of each dose.

    Further information

    This information is intended for patients receiving care in Brighton & Hove or Haywards Heath.

    The information in this article is for guidance purposes only and is in no way intended to replace professional clinical advice by a qualified practitioner.

    Publication Date: August 2019

    Review Date: September 2022

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