Many people dread being stung by a wasp, but the consequences could be more serious for older people than just the pain - with stings potentially triggering heart attacks in those with underlying heart conditions.
Around three in 100 healthy adults are known to have an allergy to insect stings or bites. If they are bitten or stung and don't get medical help immediately, their body's white blood cells overreact and attack the body itself, causing the airways to swell.
This can starve the brain of oxygen, all in as little as a few minutes.
This reaction, known as anaphylaxis, can be fatal: six people are known to die every year in the UK as a result of wasp stings. But the number could be much higher.
A lesser-known reaction, called Kounis syndrome, can even affect people who don't have a known sting allergy.
The body's normal response to a sting is to release histamine, a chemical to counteract the toxin. But with Kounis syndrome, larger amounts of histamine than normal are released in some people.
Instead of affecting the airways, this makes the blood vessels relax and then contract, sometimes sending them into spasm.
In younger, healthier people, this would not normally be felt or pose a risk. However, in older people who often have a build-up of plaques (fatty deposits) in the artery walls, these contractions cause the plaques to burst, releasing the fatty deposits into the arteries. This can cause blood clots, blockages and heart attacks.
It's thought Kounis syndrome could also be more of a risk for those fitted with stents - tiny tubes in an artery to improve blood flow to the heart. If the arteries narrow as a result of the syndrome, a stent could become blocked by a blood clot, leading to a stroke or heart attack. Although bee stings can also have this effect, wasp venom is more potent and more likely to spark Kounis syndrome.
Dr Tariq El-Shanawany, of the British Society of Immunology, says: "Kounis is basically a heart attack because of an allergic reaction." And it may be more common than doctors realise, explains Professor Anthony Frew, president of the British Society for Allergy and Clinical Immunology.
Unlike usual allergic reactions, Kounis syndrome can take up to two weeks to manifest itself, as plaques may not rupture straight away, according to a study published in the International Journal of Cardiology in 2010. Patients don't make the connection as the sting doesn't cause immediate problems.
Pharmacist Karol Pazik, who researches the effects of Kounis syndrome, estimates that 1,000 people a year are dying from "silent" wasp sting-induced heart attacks.
The key to reducing this is awareness, says Professor Frew, as doctors could change their treatment - using antihistamines, for example. As well as being alert to any heart pain following a sting, Mr Pazik suggests that older people and anyone who knows they have furred arteries or a stent fitted should be more careful to avoid being stung.
And if they do get stung, those with stents are urged to seek medical attention. Mr Pazik says: "Look out for breathlessness, confusion, disorientation, headache, nausea, blurred vision and seek medical attention if any of these symptoms appear - do not wait for chest pains."
- Daily Mail