Every summer, Anne Iarchy knows she will need to make an emergency trip to an urgent care clinic at least once.

Throughout her adult life, Anne, 52 from north London, has had an extreme reaction to insect bites. Her feet and hands swell to nearly double their usual size and the bites often become infected - requiring treatment with antihistamine tablets (the body releases histamine in response to a bite or sting, causing swelling and itching) as well as antibiotics.

Once, on a trip to Israel 25 years ago, she had to be admitted to hospital overnight after 15 bites became infected - and she needed intravenous antihistamines.

On another occasion, she was bitten on her eyelid, leaving her eye painful and so swollen that she couldn’t open it for four days. She missed out on being a volunteer for the London 2012 Olympics because a bite on her foot meant she couldn’t put her shoe on, let alone stand because of the swelling and pain.

‘Each summer I get an infected bite at least once, often on my foot, ankle, hand or arms probably as they are the most exposed,’ says Anne, who is a health coach.

‘I usually get bitten at the park or golf course,’ says keen golfer Anne. ‘I apply strong insect repellent to try to stop it from happening and my arms and legs are fully covered, but they still manage to bite me. I know it could be worse if I didn’t do that, though.

Why do some people such as Anne react to bites in this way? Blame the individual’s immune system - and how often they are bitten: you tend to react more if you’re not bitten much, explains James Logan, a professor of medical entomology at the London School of Hygiene and Tropical Medicine.

‘Over time, your body can become immune and not react very much,’ he explains.

Some of us do get bitten more than others, which could be down to our smell, he adds. ‘People who don’t get bitten much produce natural repellents in their body odour which act as their own natural defence system.’

These chemicals (known as aldehydes and ketones), are thought to be be down to genetic and environmental factors, as well as to the types of bacteria that we all have living harmlessly on our skin.

‘Some of these chemicals are released in sweat and they can also be eaten by the bacteria on the skin which, in turn, produces more of these chemicals - in theory making bites even less likely,’ explains Professor Logan.

Body size can also be a factor in whether you are likely to be bitten. A study led by Professor Logan, published in the journal BMC Public Health in 2010, found that midges were more likely to bite men who were tall and women with a larger body mass index (BMI).

‘We don’t really know why it is. It may be because there is more of them to bite, or their bodies are producing more attractants, such as carbon dioxide, in their breath,’ he explains, adding that the gas is a strong signal to insects that an animal or human is nearby. It is thought that taller people have larger chests and lungs, meaning they may take in more oxygen and breathe out more carbon dioxide.

Research also suggests that people with blood type O are most attractive to mosquitoes. In research, published in the American Journal of Entomology in 2019, mosquitoes were given the option to feed on A, B, AB and O blood types and they chose type O more frequently. It is thought they ‘sniff out’ O blood type, though how and why is not clear.

In fact, this keen sense of smell could be harnessed to diagnose different conditions in future. Professor Logan is using insects as sensors in his lab to work out the smell of different diseases. ‘Insects live in a hidden world of odour which is like a hidden world of communication,’ he explains. ‘We’re building machines – basically sniffer robots – to do the job of an insect by detecting if someone has malaria, and the hope is that one day this could detect other conditions, including cancer.’

For most of us, the painful, itchy, swollen areas which develop around the bite or sting usually resolve after a few days and can be managed at home with antihistamines and soothing creams. The swelling - a sign of inflammation - occurs as part of the immune response as our body releases histamine and other chemicals to seal the area and respond to any harmful substances that have broken through the skin.

However, there is a risk that bites and stings become infected. Signs include the area becoming hot, red, painful and producing pus. People with poorly controlled diabetes are at particular risk of infected insect bites and stings because of their high blood sugar levels. ‘Bacteria like feeding on sugar, so when someone with diabetes has a cut or bite they need to keep a close eye on it because infections can develop more quickly,’ advises Brendon Jiang, a pharmacist based in Oxfordshire and vice chairman of the Royal Pharmaceutical Society’s English Pharmacy Board. (The condition also affects the immune system, making it harder to fight off infections.)

If the raised, red lump doesn’t start to go down after a couple of days, draw around the area and see if it spreads, suggests Professor Logan. If the infection spreads, you may need to see a doctor and you may need antibiotics. A study published last year in BMJ Open found that two thirds of people who sought help for insect bites from out-of-hours primary care in Birmingham between July 2013 and February 2020 were prescribed antibiotics.

But Dr Sam Finnikin, a GP based in Birmingham, who led the research, says insect bites often don’t require antibiotics, and this is especially concerning in light of antibiotic resistance.

‘Clinicians find it difficult to decide which insect bites would benefit from antibiotics,’ says Dr Finnikin, who is also a researcher focused on clinical decision making at the University of Birmingham. ‘We know the vast majority improve without antibiotics, but some infected bites may get better slightly quicker with them. Usually, the immune system can deal with infections unless there are concerns about sepsis.’ Any infection, including a bite, can potentially develop into this life-threatening condition where the immune system overreacts and damages the body’s own tissues and organs.

However, he adds: ‘It’s important that antibiotics aren’t given if there’s no infection as they won’t have any benefit and can cause side-effects such as thrush and diarrhoea.’ Sometimes people are given antibiotics for an insect bite once, then they mistakenly feel they need them every time, he says,

Anne Iarchy’s reactions are due to an allergy to the venom in bites and stings, which can cause much nastier symptoms as the body overreacts, explains Jiang.

A serious allergic reaction - anaphylaxis - can cause swelling of the airways or around the mouth and face, dizziness, sweating, difficulties breathing and a drop in blood pressure. ‘If you experience any of these signs then call an ambulance,’ says Professor Logan. ‘Usually it happens immediately but, in rarer cases, it could come on a couple of hours later. If people have known serious allergic reactions, they should carry an EpiPen.’

How to treat bites and prevent them in the first place

GP Dr Finnikin recommends keeping a supply of over-the-counter antihistamine tablets and creams, and hydrocortisone cream which contains a mild steroid and can relieve itching. Scratching the affected area can increase the chance of infection because it can make the break in the skin worse and introduce bacteria from fingernails into the wound.

‘There’s a scratch-itch cycle. When we scratch, it causes more histamine to be released and the chemical then triggers more itching,’ explains Dr Finnikin. Massaging or rubbing the area is better and cooling gels can soothe the skin. Look for products containing ammonia, which neutralise some of the venom from a bite or sting, because venom is usually acidic while ammonia is alkaline. Pharmacist Brendon Jiang recommends using cold compresses to reduce swelling and says bite relief pens, which deliver small electric shocks to the affected area, can be beneficial. This distracts nerve cells from sending itch signals to the brain, relieving itchiness.

Where possible, remove the sting with tweezers or fingers, and use a twisting method to get ticks off the body, he adds.

To avoid bites and stings, Professor Logan recommends insect repellents containing DEET, IR3535, oil of lemon eucalyptus (OLE) or Picaridin. ‘These work well on mosquitoes, midges and ticks,’ he says, adding that it’s best to avoid going out at dusk, when most mosquitoes are out. And avoid walking through long grass (where ticks are often found) and cover up with long trousers, long socks and long-sleeved tops.