Mosquito bites: how to treat them and stop the itch

A mosquito bite is one of the most universal summer annoyances: it itches, swells, wakes you up at night and, if you scratch it, can become infected. In this pharmacist-written guide I explain exactly what to do in the first few minutes, which pharmacy products really work and when it makes sense to move up to an oral antihistamine or see a doctor.

Why a mosquito bite itches so much

A mosquito bite is a local allergic skin reaction caused by mosquito saliva. When the mosquito bites, it does not just puncture the skin – it injects saliva containing anticoagulants so your blood does not clot while it feeds. That saliva is what triggers the local allergic response: your immune system releases histamine, which causes the red wheal, itching and swelling.

• Immediate wheal (15–20 min): type I reaction mediated by IgE and mast cells. This is the classic red wheal.
• Late reaction (24–48 h): type IV reaction mediated by T lymphocytes. A firm papule appears that can last for days.
• Huge individual variability: some people hardly react at all and others (especially children) develop very large, reactive wheals.
• Tolerance over time: with repeated exposure many people develop tolerance and reactions become milder with age.

What to do in the first 5 minutes after a mosquito bite

Acting quickly makes a real difference to how much a mosquito bite bothers you later. As soon as you notice the bite you should:

• Wash with soap and water: this removes any mosquito saliva left on the surface and reduces the risk of infection from contamination.
• Apply something cold locally for 10–15 minutes: ice wrapped in a cloth, a cold compress or very cold water. This reduces vasodilation, swelling and itching.
• DO NOT rub or scratch: this worsens the reaction and opens the door to secondary infection from bacteria under your nails.
• Apply a topical soothing product straight away: see options below.

Topical treatments for mosquito bites: what works and how to choose

I usually think in three levels of topical treatment depending on how intense the itch is and the person's age:

• After Bite Original (ammonia): After Bite Original, the classic stick. The ammonia helps neutralise the acidity of insect venom. It gives rapid itch relief. Suitable for adults and children from 2 years.
• After Bite Gel Xtreme (longer-lasting action): After Bite Gel Xtreme has a more prolonged effect in an easy-to-use gel format. I reserve it for more reactive bites or suspected tiger mosquito bites.
• After Bite Pediatric (babies and pregnancy): After Bite Pediatric with natural ingredients, suitable for babies, children and during pregnancy.
• Fenistil Gel (topical antihistamine): Fenistil Gel 30 g contains dimetindene, an antihistamine applied directly to the skin. It is my preferred option if the bite is very reactive or if you have several bites.
• Fenistil Roll-On (portable format): Fenistil Roll-On 8 ml, compact format to keep in your bag or rucksack. Same active ingredient as the gel.
• Mild topical steroid (widespread reactions): hydrocortisone 1% cream for more intense reactions. Ask your pharmacist for advice.

When to step up to an oral antihistamine for mosquito bites

A topical soothing product is enough in around 90% of mosquito bites. I suggest stepping up to an oral antihistamine when:

• You have several bites at once: a cream or stick will not adequately cover 8–10 different areas.
• The reaction is very extensive: wheal larger than 3–5 cm, or swelling that affects function (hand, eyelid, joint).
• You are very reactive to bites: previous history of large wheals and disabling itch.
• The bite interferes with sleep or work: taking an oral antihistamine at night reduces itching while you sleep.

The most commonly used oral antihistamines are: cetirizine 10 mg once daily, ebastine 10 mg once daily, bilastine 20 mg once daily. All are available without prescription in many countries but in the UK you should follow MHRA guidance and local availability. Ask your pharmacist to help you choose the most suitable option according to age, other medicines you take and whether you need to drive (bilastine and ebastine are among the least sedating).

Mosquito bites in children and babies: precautions

Children often have more intense reactions than adults because their immune system is more reactive. The key points I emphasise are:

• After Bite Pediatric as first choice: After Bite Pediatric, with natural ingredients and suitable from baby age. It does not contain ammonia, which can irritate delicate infant skin.
• Slightly longer cold application: 15–20 minutes with cold compresses helps especially in children.
• Keep nails short: this reduces damage if the child scratches and lowers infection risk.
• If the reaction is extensive or there are several bites: speak to your paediatrician before giving an oral antihistamine (dose must be adapted to weight).
• Late reactions are common: in children large wheals appearing at 24–48 hours are frequent. This is NOT usually a severe allergy but an immature immune response. It settles within 3–5 days.

Mosquito bites during pregnancy

Pregnancy does not increase your risk of being bitten by mosquitoes but it can increase skin reactivity because of immune changes:

• Safe topical soothing options: After Bite Pediatric (natural ingredients, suitable in pregnancy) and Fenistil Gel (authorised for use in pregnancy).
• Cooled compresses or ice packs: my first-line recommendation as they have no contraindications.
• Oral antihistamines in pregnancy: always check with your obstetrician. Cetirizine and loratadine have acceptable safety profiles in pregnancy but should only be used on medical advice.
• If you are bitten by a tiger mosquito in an area with active dengue or Zika transmission: seek medical advice immediately. Zika infection during pregnancy can cause fetal malformations.

For a full guide on insect repellents during pregnancy, have a look at my dedicated article on mosquito repellents in pregnancy and breastfeeding.

How to stop a mosquito bite becoming infected

Bacterial secondary infection is the most common complication of insect bites, almost always due to scratching:

• Avoid scratching completely if you can: scratching breaks the skin barrier and introduces bacteria from under your nails (Staphylococcus aureus, Streptococcus).
• Keep nails short and clean: this reduces damage if you scratch unconsciously.
• Cover very itchy bites with a plaster: this simple mechanical barrier is especially useful in children who scratch while asleep.
• If there are scratch marks use a topical antiseptic: chlorhexidine or povidone iodine to clean the area thoroughly.
• Warning signs of infection:

When to seek medical advice

Most bites settle on their own with a topical soothing treatment. Seek medical advice — urgent care or your GP depending on severity — if you notice:

• Fever after a recent bite in an area with active dengue or Zika: possible viral transmission.
• Joint pain, muscle pain or pain behind the eyes after a bite in an endemic area: symptoms compatible with dengue.
• A very large reaction: a welt larger than 10 cm, or swelling that affects function, such as the mouth, eyelid or hand.
• Signs of secondary infection: pus, heat, throbbing pain, or red streaks running towards the lymph nodes.
• Systemic reaction: widespread hives, breathing difficulty or low blood pressure. This may be anaphylaxis — seek emergency help immediately.
• A bite in a child with a high fever and marked drowsiness or weakness.

Myths and facts about treating insect bites

• “Applying saliva relieves itching”: false. It increases the risk of infection from mouth bacteria.
• “Heat or burning the bite cures it”: a popular myth with no evidence. Cold can help; heat may make it worse.
• “Ammonia is safe on children’s skin”: false. After Bite Original is NOT recommended for babies — use After Bite Paediatric instead.
• “Bites disappear on their own within 24 hours”: it depends. Common mosquito bites often do, but tiger mosquito bites can last 5–7 days.
• “Vinegar cures itching”: it may give mild relief as it evaporates, but it is not a real treatment.
• “Eating garlic prevents bites”: a myth with no evidence.
• “Large welts in children mean a serious allergy”: in most cases, NO. It is usually an immature immune response and settles on its own.

Essential summer bite-care kit

If you are staying somewhere with high mosquito pressure, such as the Mediterranean coast, rural areas or campsites, this is the minimum viable bite-care kit:

• Classic topical soothing treatment: After Bite Original for adults + After Bite Paediatric for children and pregnancy.
• Topical antihistamine: Fenistil Gel 30g for use at home, or Fenistil Roll-On 8ml to carry with you.
• Oral antihistamine: cetirizine or bilastine for larger reactions.
• Hydrocortisone 1% cream: for more reactive bites. Ask a pharmacist before use.
• Plasters and gauze: to cover the area and help prevent scratching in children.
• Repellent: essential to avoid further bites. Relec Extra Strong, Relec Kids or Goibi Citriodiol.

My final recommendation as a pharmacist

This is the plan I use in pharmacy when someone comes in with mosquito bites:

• Classic case — 1–3 common mosquito bites: After Bite Original + local cold application. Usually settles within 2–3 days.
• Tiger mosquito or a larger reaction: After Bite Xtreme or Fenistil Gel. If itching keeps you awake at night, consider an oral antihistamine.
• Children and pregnancy: After Bite Paediatric is always the safer choice.
• Travel kit: Fenistil Roll-On + After Bite Original as your minimum viable option.

And the golden rule I repeat every time: DO NOT scratch. Itching is unpleasant, but it usually passes within 2–7 days. A bacterial infection caused by scratching lasts longer, may require antibiotics and can leave a scar. Before scratching, apply local cold + a topical soothing treatment. It is the simplest change that improves the outcome.

If you also want to prevent bites before they happen, read our guide to the 5 best pharmacy mosquito repellents for 2026 and, if you are in an area with tiger mosquitoes, our specific guide to tiger mosquitoes in Spain.

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