If you are stung by an insect, such as a wasp, the area around the sting will become swollen, go red and a raised mark will form. The raised mark is called a weal.
Some people may have further symptoms after an insect sting, although most people will not have severe symptoms. The reaction can be classed as:
- a minor localised reaction – this is normal and does not require allergy testing, although the affected area will often be painful for a few days
- a large localised reaction (LLR) – this can cause other symptoms such as swelling, itching and a rash
- a systemic reaction (SR) – this often requires immediate medical attention as it can cause a potentially life-threatening allergic reaction (anaphylaxis)
An allergic reaction occurs when the venom from the sting triggers the release of chemicals in the body, such as histamine. The chemicals can affect the blood vessels in two ways:
- they can widen, causing a drop in blood pressure
- they can leak, causing swelling, particularly in the mouth and on other parts of the skin
People who have a systemic reaction (SR) due to an insect sting may experience much more severe symptoms and will need to be referred to an allergy specialist for testing and treatment. However, although insect stings are a common cause of anaphylaxis, it is rare to experience anaphylaxis after an insect sting, and it is rarely fatal.
Large localised reactions and systemic reactions are described in more detail below.
Large localised reaction (LLR)
If you have a large localised reaction (LLR) after being stung by an insect, a large area around the sting will swell up. The area may measure up to 30cm (12in) across, or your entire arm or leg could swell up.
The swelling will usually last longer than 48 hours but should start to go down after a few days. The sting will be painful but the swelling will not be dangerous unless it affects your airways.
If you are stung many times by one or more insects, your symptoms will be more severe because a larger amount of venom will have been injected.
You may have an LLR several hours after being stung. This could include:
- a rash
- nausea
- painful or swollen joints
Systemic reaction (SR)
A systemic reaction (SR) is often less severe in children than in adults, and children are less often referred for venom immunotherapy (see treating stings for more information). It is rare for an SR to be fatal, especially in children, although someone with an existing heart or breathing problem is at increased risk.
It is also more likely that someone will have an SR if they have been stung before (sensitised), especially if it was recently. People who have been sensitised to bee stings are more likely to have an SR than people who are stung by wasps.
If you have any of the following symptoms immediately after being stung, seek emergency treatment. Call 999 and ask for an ambulance immediately as this kind of reaction can be fatal:
- swelling or itching anywhere else on your body
- a skin reaction anywhere else, particularly pale or flushed (red or blotchy) skin
- wheezing, hoarseness or difficulty breathing
- a headache
- nausea, vomiting or diarrhoea
- a fast heart rate
- dizziness or feeling faint
- difficulty swallowing (dysphagia)
- a swollen face or mouth
- confusion, anxiety or agitation
Read information about treating insect stings.
