We are all very aware that being stung by a bee or wasp causes symptoms at the site of the sting. This is entirely normal and does not suggest that the sufferer has an allergy. Bee or wasp venom is capable of producing this effect in all of us.

An area of localised swelling up to the size of a saucer, accompanied by pain and lasting up to seven days, may occur following a bee or wasp sting in between 10-15% of adults. On its own this type of reaction does not indicate true allergy and is not dangerous unless the airway is affected by swelling from a sting in the mouth or throat. This type of reaction is known as a 'large local reaction' (LLR) and is caused by substances that induce an inflammatory reaction which develops over a few hours and settles in a day or so. These substances are not the same as those that cause allergy in susceptible people.

Bee and wasp allergy

Bees and wasps are capable of causing allergic reactions in susceptible people because of certain enzyme proteins contained in the venom. A true allergic reaction to a bee or wasp sting is more immediate and more severe. An allergic reaction to a bee or wasp will probably cause a large localised reaction with pain and swelling within minutes of the sting, but will also include one or more of the following symptoms that typically start within ten minutes of being stung.

Allergy to the venom of either a bee or a wasp is thought to be induced by a previous sting. In other words the first sting capable of inducing an allergic reaction is the second sting.  The enzyme that causes bee allergy is not the same as the enzyme that causes wasp allergy. Patients with an allergy to either a bee or a wasp often ask if this means they are more likely to be allergic to the other. Although this can occur (when someone happens to be allergic to both substances) but in practice it is rather unusual.

Allergy tests

Patients are often surprised when told that bee or wasp allergy skin prick or blood tests are not 100% accurate. For example, from studies undertaken in the UK using standard allergy tests we know that between 5% and 10% of adults have antibodies to wasp venom and will therefore give positive results to allergy tests. However, no more than 5% of these same adults have ever had allergic symptoms following a sting.

This is not too surprising to allergy specialists; the same differences are seen for other allergies. Evidence that the patient has an antibody (i.e. a positive skin prick or RAST blood test) is not evidence that the patient has an allergy it is evidence of the patient is capable of getting the allergy and this is called sensitisation. People can have positive allergy tests for many years, and even for an entire lifetime, without ever developing the allergy.

A good example of this is found when people with a good history of allergy to bee or wasp are studied by the standard allergy blood test. This will show up to 30% of false positive results - that is patients with antibodies to both bee and wasp, but who are only allergic to one of them. Patients are rarely allergic to both bees and wasps, so allergy tests are very capable of giving a false impression.

Increasing the fear
It is unfortunate that false positive tests for bee or wasp allergy are not uncommon. It would be very helpful to have a test that could accurately rule out bee or wasp allergy in those terrified by the idea of it. Bee and wasp allergy tests are very useful to confirm allergy in patients giving a good history of allergic symptoms following a sting. However, patients who ask to be tested but who have never experienced clear symptoms of allergic reaction need to be warned that there is a chance that their test result could be falsely positive and thereby risk increasing their fear rather than reducing it.

At the other extreme, patients with a definite history of bee or wasp allergy very occasionally have a falsely negative allergy blood or skin test. Scientists believe that this happens because a different kind of allergy mechanism may cause the condition in some cases.

So a positive allergy blood or skin test cannot prove with certainty that someone is allergic to bee or wasp stings. And a negative allergy blood or skin test cannot prove with certainty that someone is not allergic to bee or wasp stings! The only certain tests are either a provocation test with a real sting or a subcutaneous injection using pure bee or wasp venom! Such tests are impractical for regular patient care, but they are used in research and occasionally be specialised allergy units.

Anaphylaxis

Severe allergy to the sting of a bee or wasp is thankfully rare. Anaphylaxis is the most severe form of allergy and can be life threatening. Typically there is a dramatic, rapid and diverse occurrence of any combination of the various symptoms known to be associated with immediate allergy, and if severe, an attack may be accompanied by asthma, laryngeal oedema or circulatory collapse

People known to have had an a true allergic reaction to bee or wasp (and not just a large local reaction to a sting), and who are therefore thought to be at risk of further anaphylaxis, may be advised carry injectable adrenaline (e.g. EpiPen^®) particularly when they are in a situation when they face a risk of being stung.  

However, certain facts may be reassuring to such patients. Firstly, they may believe that death as a result of bee or wasp stings is commoner than it is. In fact, on average, 2-6 deaths per year from allergy to bee or wasp stings occur in the UK and this is similar to the number who die as a result of being struck by lightening. The chance of being murdered is over 100 times greater than dying from a bee or wasp sting. 

The other mistaken belief is that each time there is a sting, the reaction is worse. This may cause someone who has had a true allergic reaction to a bee or wasp (and in some cases someone who has had nothing more than a large local reaction) to be more anxious than they need to be.

The real facts concerning what happens after someone suffers an allergic reaction after a bee or wasp sting are far more reassuring:

So anyone who thinks they have experienced a true allergic reaction to a bee or wasp sting should discuss what happened with their doctor. If the doctor diagnosis an allergy, then the patient may be advised to carry self-administered adrenaline (e.g. EpiPen, Anapen) in case of a further bad reaction. 

Patients often believe that allergy tests can predict both the likelihood and the severity of a future sting. Unfortunately this is not the case and if the standard allergy tests are interpreted in this way then false conclusions may be reached. The only tests that can make some sort of a prediction are either a provocation test with a real sting or a subcutaneous injection using pure bee or wasp venom. 

How to cope

People with wasp or bee allergy should avoid situations where they risk getting stung. If a wasp or bee is seen, remain calm and still, and do not try to wave it away or swat it. Wasps and bees rarely attack people tending to sting only if disturbed or cornered. It therefore follows that people who tend to ignore them are less likely to be stung.  Beekeepers are much more likely to suffer from bee sting allergy, more than a quarter will have had at least one reaction.

Certain people appear to attract bees and wasps, this may be due to their own chemical secretions. Bees and wasps are also drawn to perfumes and bright colours, so white clothing is preferable. Avoid using perfume, after-shave or scented toiletries when you are going to be in an 'at risk' area. Wasp or bee allergic people should avoid sugary drinks, and sweetened foods when eating outdoors, other foods should be kept well covered before being eaten. On the picnic table, special scented candles, or cloves stuck into a potato, can be used to repel stinging insects. Never walk on grass barefoot and if clothing has been left outdoors, shake it carefully before putting it back on.

Bees will leave their sting behind in the skin, wasps do not do this. If stung by a bee, flick away the sting being careful not to squeeze the sting and inject more venom. For either a bee or wasp sting, apply ice or a cold compress to the sting, and rest the affected part. Any sting reaction, allergic or not, will be lessened by avoiding undue stress or exertion. Exercise and heat (e.g. a hot bath) should be avoided as either may increase the severity of any reaction. For the vast majority of bee or wasp stings, these are the only measures that are needed.

For mild allergic reactions in adults or older children two tablets of chlorphenamine (Piriton®) can be helpful. The treatment may casue drowsiness, but in a fretful child this might be an advantage. This would be suitable in someone with a previous history of allergy to the insect with localised and very itchy swelling several inches across. More severe or generalised reactions, for example with all-over itching or rash, might be better treated with an injection of antihistamine and medical help should be considered.

Severe reactions with any hint of faintness, change of skin colour, clamminess or breathing difficulty should receive urgent medical attention. Those with known allergy to the insect concerned may carry a pre-loaded adrenaline syringe and if the situation warrants it, (see under anaphylaxis) this should be given first, the seeking of medical advice should then follow.

Desensitisation treatment

Desensitisation treatment for bee or wasp venom allergy may be suitable for certain people who have suffered a severe and generalised allergic reaction to a bee or wasp. Although the treatment is very successful (after treatment, a venom dose equivalent to two stings can be given without effect) it is tedious and time-consuming and suitable cases for treatment need to be selected with care. For example, those whose work or hobby brings them into close contact with bees or wasps (e.g. farmers, gardeners, beekeepers) and who if untreated might be forced to change their occupation or hobby may be especially suitable for treatment. So too might be someone with a severe allergy and living in a very remote location.

To be suitable for treatment, the sufferer should have good evidence of allergy to the insect concerned. At least one previous allergic reaction should have been sufficiently severe to cause either a breathing upset (throat narrowing or wheezing attack), a fall in blood pressure, or collapse. Angioedema (allergic swelling), dizziness, nausea, sweating or a choking sensation during a previous attack are other symptoms that may be taken into account when assessing suitability for desensitisation treatment.

Mosquitoes and horseflies

Mosquitoes are found in most parts of Europe, in North America, Asia and Japan. When mosquitoes feed, they inject saliva into the skin, which has been shown to lead to allergy in some people.

Not all of the minor itchy skin reactions that are caused by the bite of the mosquito are due to allergy. When larger local reactions occur, an element of allergy may be present. These are of two main types. Rapid onset (within minutes) weal and flare reactions and delayed (several hours later) itchy papules are common.

In most people who develop allergy to mosquites, the problem seems to start in childhook. Whilst mild reactions are far more common, generalised reactions, including rashes and swellings, nose and eye symptoms and wheezing have been reported. Anaphylactic shock following mosquito bites is rare, but it has been reported.

There are very occasional reports of anaphylaxis caused by horseflies.

Other insects

Adapted from NHS Clinical Knowledge Summaries