Insect bites and stings: normal reaction, allergy and when to worry

Dinner in the garden on an August night comes at a price. The light fades, you light the candle and, without warning, something starts circling your ankles. Next morning you wake up with three lumps that itch like mad. Or maybe you trod on a wasp barefoot in the sand and your foot swelled up within ten minutes. Insect bites and stings are the soundtrack of summer on the Costa Brava and, luckily, they almost always come to nothing more than a passing nuisance.

The hard part is telling when a bite is only that, an annoying local reaction, and when it hides an allergic reaction that really does need attention. At Clínica Eupnea, in Palamós (Baix Empordà), the allergology clinic sees people every summer who are frightened by dramatic swelling that carries no danger at all and, on the other hand, people who had a genuinely serious reaction and thought nothing of it. Let's look at how to recognise each case, what you can do at home and when it is worth taking seriously.

What happens in the body when an insect bites you?

Not all insect bites and stings are the same, and understanding that helps you keep a cool head. Mosquitoes, in fact, do not sting: they feed. When a female sinks in her proboscis, she injects a little saliva containing anticoagulants so that the blood does not clot while she drinks. Your body detects these foreign proteins and releases histamine, and it is the histamine, not the insect, that produces the lump, the redness and the characteristic itching.

Wasps and bees are playing a different game: they are not feeding on you, they are defending themselves. They drive in a sting and inject venom, which is why their sting hurts at once, like a burn, rather than the dull itch of a mosquito. The amount of venom is small and, in most people, causes nothing more than pain and local swelling that fades in a day or two. The trouble begins when some people's bodies react to that venom out of all proportion. This is where allergy starts, and it is something quite different from the normal reaction we all have.

Normal reaction, large local reaction and allergic reaction

This is the part worth reading to the end. A small lump, half your arm swelling up and struggling to breathe are not the same thing, even when the same bite caused all three. Telling them apart is what decides whether you can deal with it at home or need to call a doctor.

The normal local reaction

This is what happens to almost everyone. A red lump, ringed by a little swelling, that itches or stings and fades over a few hours or, at most, a couple of days. It has no medical importance and heals on its own. The size depends on the insect and on your skin, but it stays around the spot where you were bitten.

The large local reaction

Some people develop what doctors call a large local reaction: the area swells far more than seems reasonable, sometimes the whole forearm or half a foot, and turns red, hot and firm, and it can last several days. It is alarming to look at, especially on the face, but it is not a dangerous allergy and does not usually progress. It is managed with cold, antihistamines and, if the doctor advises it, a corticosteroid. What sets it apart from an infection is timing: the reaction appears straight away, whereas an infected bite gets worse after two or three days and tends to ooze pus.

The generalised allergic reaction

Here everything changes. In a genuine allergic reaction, the body responds not just around the bite but everywhere. Weals or hives (urticaria) can appear on skin far from where you were stung, along with itching on the palms of the hands or the scalp, swelling of the lips and eyelids and, in severe cases, difficulty breathing and a feeling of faintness. It is the same logic by which the body can react to triggers as varied as the cold, which we cover in our article on cold allergy: the immune system fires when it should not. This generalised response is the mark of a true insect sting allergy, and it should set off every alarm, because it can progress to anaphylaxis. It happens almost always with wasp and bee venom, and very rarely with mosquitoes.

Which insects bite and sting on the Costa Brava in summer

In our area, between the sea, the wetlands and dinners eaten outdoors, the list of insects that visit us in summer is fairly predictable:

• Mosquitoes, including the tiger mosquito, ever more common along the Girona coast. They bite mostly at dawn and dusk and leave lumps that itch a great deal, but they are rarely dangerous.
• Wasps and bees, responsible for almost every serious allergic reaction. Wasps come to food and sweet drinks; bees sting when they feel trapped.
• Horseflies, those big flies of field and beach whose bite is painful and bleeds a little.
• Ants and other small creatures you can meet in the sand or on the grass.
• Ticks, which neither bite nor sting as such but latch onto the skin; what matters is removing them early and whole.

Anaphylaxis: the emergency you need to recognise

Anaphylaxis is the most severe form of allergic reaction and it is a medical emergency. It can set in within minutes of the sting and affects several organs at once. The signs you cannot ignore are:

• Difficulty breathing, wheezing in the chest or a feeling that your throat is closing.
• Swelling of the tongue, the lips or the throat, and a hoarse voice.
• Hives spreading over the whole body, with intense itching.
• Dizziness, a racing pulse, cold sweat or a feeling of fainting.
• Nausea, vomiting or sudden stomach pain.

Faced with one or more of these signs, call 112 without waiting. Anyone who already knows they are allergic and carries an adrenaline auto-injector should use it on the thigh at once: adrenaline is the only treatment that stops anaphylaxis, and antihistamines cannot do the job. Even after using it you still need to go to hospital, because the reaction can flare up again a few hours later.

How to treat a bite or sting at home

The vast majority of insect bites and stings clear up with four simple steps:

• Remove the sting if a bee got you. Do it straight away, scraping it out with a fingernail or the edge of a card; do not grab it with tweezers or your fingers, as you would squeeze the little venom sac and inject more.
• Wash the area with soap and water and apply cold (an ice pack wrapped in a cloth) in ten-minute spells. The cold brings the swelling down and numbs the itch.
• If it itches badly, an oral antihistamine or a mild corticosteroid cream will help. The pharmacy "after-bite" products ease it too.
• Do not scratch. It is the hardest advice to follow and the most important: scratching breaks the skin and opens the door to infection, above all in children.

One habit many people carry from childhood: the old trick of dabbing on ammonia, vinegar or saliva does little, and rubbing the spot with a coin does even less. Cold and time are what do the work.

How to prevent insect bites and stings

There is no way to make yourself invisible to mosquitoes, but a few habits go a long way towards cutting down insect bites and stings through the warm months:

• Use a repellent with DEET or icaridin on exposed skin and reapply it as often as the label indicates.
• At dawn and dusk, when mosquitoes are at their busiest, cover up with light-coloured clothing, long sleeves and long trousers whenever you can.
• Avoid sweet perfumes and, when you eat outdoors, cover sugary drinks: they draw wasps towards the can or the glass.
• At home, fit insect screens on the windows and empty any container of standing water in the garden or on the terrace, which is where the tiger mosquito breeds.
• If you walk through woodland or tall grass, wear long clothing and check your skin when you get back to rule out ticks.

These precautions count double for children and for anyone who has already had a strong reaction: in those cases, avoiding the bite is half the battle.

When to see an allergist

Most bites need no doctor at all. There is, however, one situation that does warrant it and that people often overlook: having had a generalised reaction after a wasp or bee sting, whether hives all over the body, swelling far from the bite or any symptom of anaphylaxis. If it has happened once, the risk that it recurs and is worse next time is real, and it is worth investigating.

The allergist in Palamós can confirm an insect sting allergy with skin tests and a blood test and, where needed, recommend venom immunotherapy: a course of injections that teaches the body to tolerate the sting and dramatically lowers the risk of a severe reaction. It is the same principle we explain in the article on the allergy test, and it fits within the broader approach you will find in our guide to allergies: origin and impact. You should also seek advice if your bites often become infected, if you get very large local reactions that hold you back or, quite simply, if the fear of a sting is shaping your summer.

If you would like to check this information against independent medical sources, you can read the MedlinePlus page (US National Library of Medicine), the guide from the UK National Health Service (NHS) or the patient information from the American Academy of Allergy, Asthma & Immunology (AAAAI).

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