Insect Repellent for Thailand: The Mosquito Sprays That Work and What to Buy There

The health agencies agree on the ingredients and differ a little on strength. The CDC's Thailand page says to use 20% or more DEET for protection that lasts several hours, and lists picaridin, oil of lemon eucalyptus (also sold as PMD), IR3535 and 2-undecanone as the other ingredients that work on mosquitoes. Thailand's Department of Disease Control gives the same 20% DEET figure in its own leaflet for travelers.

The UK's travel health service, NaTHNaC, goes higher. It recommends 50% DEET for anyone over two months old who tolerates it, and says there's no gain in how long it lasts beyond 50%. For picaridin, which British labels call icaridin, it says at least 20%. It rates oil of lemon eucalyptus and IR3535 as working for a shorter time than DEET, so they need putting on more often.

A higher percentage buys you time, it doesn't repel harder. A 12% lotion and a 50% spray both keep mosquitoes off, and the difference is how soon you have to put more on. That matters most in Thailand's heat, because NaTHNaC notes that sweat, humidity and swimming all shorten the cover, and that most people apply about half the amount a product was tested with.

My pick for most trips is a 20 to 30% DEET or 20% picaridin spray from home, plus a Soffell lotion bought on arrival for the day bag. Picaridin is the one to choose if you dislike the feel and smell of DEET, and it's kinder to your gear, since NaTHNaC warns that DEET can damage synthetic fabrics.

Buy the everyday bottle in Thailand and bring the strong one. Repellent is sold in 7-Eleven, pharmacies, Watsons, Boots and supermarkets across the country, and at ฿59 to ฿79 a Soffell costs a fraction of what a travel shop charges at home. In a shop, ask for ya gan yung (ยากันยุง), and look for Soffell's pink and orange packaging.

What the Thai shelf doesn't give you is strength. The listings I read from HomePro, Watsons and King Power carry Soffell at 12 to 13% DEET and OFF! at 15%, and none of them shows a 20% DEET or a picaridin spray. A pharmacy may stock something stronger, but you can't plan a jungle trip around that. If your clinic named a strength, or you're heading for forest, pack it.

The same goes for children's and plant-based formulas. If you want a specific one, bring it, because Thai DEET products are labeled for age four and up and the lemongrass sprays on the shelf are short-lived.

Thailand has mosquitoes all year, in cities as well as the countryside, and more of them in the rainy season from June to October, which is also when dengue peaks. The dengue mosquito is the one a typical trip meets. It lives around towns and buildings and is active in the daytime, which is why NaTHNaC tells travelers to avoid bites particularly during daytime hours. The CDC also rates Thailand as having an elevated risk of chikungunya, spread by the same daytime mosquitoes.

The evening and night biters matter in the countryside. The mosquitoes that carry Japanese encephalitis bite between dusk and dawn, mainly in the countryside around rice fields, swamps and marshes, and the risk peaks from May to October. Malaria mosquitoes are a forest matter, covered below.

In practice, wear repellent through the day in the wet months, and add long sleeves and another coat of repellent at dusk whenever you're near forest, water or farmland. Jungle stays, waterfalls, mangroves and national parks such as Khao Sok are where I'd carry the strong bottle.

Put sunscreen on first and let it settle, then repellent on top. Cover all exposed skin, ankles and feet included, and don't put it under clothes. Use your hands to spread it on your face and keep it away from your eyes, mouth and any cuts.

Reapply sooner than the label promises. NaTHNaC's rule is to put more on when the mosquitoes start to take an interest, and after swimming or heavy sweating. With a 12 to 15% Thai lotion on a humid day, I'd plan on every few hours.

Wash it off when you're in for the night, and wash your hands after applying so it stays out of your food and off your phone screen and sunglasses.

The rules here depend on whose guidance you follow. Thai labels on Soffell and OFF! say not to use them on children under four, and the Thai Department of Disease Control says children under four should use a repellent with less than 10% DEET. The UK's NaTHNaC allows DEET at up to 50% from two months of age. The CDC says oil of lemon eucalyptus and PMD shouldn't be used on children under three.

For a baby or toddler, the simplest plan is to bring a product your own doctor or travel clinic is happy with, and lean on cover. Dress children in long, loose clothes, put netting over the stroller or carrier, and keep them in screened or air-conditioned rooms at dusk. An adult should put the repellent on their own hands first and then onto the child, and never onto a child's hands, which end up in the mouth.

If you're pregnant, NaTHNaC says DEET at up to 50% can be used in pregnancy. It also lists a risk of Zika in Thailand and advises pregnant women to discuss the trip with their doctor before they travel, so have that conversation early.

Repellent is one layer. The Thai Department of Disease Control's advice is long sleeves, long pants and loose, light-colored clothes, and a screened room or a bed net to sleep in. An air-conditioned room with the windows shut does the same job. Clothes treated with permethrin keep working through several washes, and permethrin never goes on skin.

In a fan bungalow, a plug-in vaporizer helps at night, and mosquito coils are for outdoors only. Check the net for holes and tuck it under the mattress.

NaTHNaC lists what has no evidence behind it, and that's garlic, vitamin B, electronic buzzers, phone apps and tea tree oil. Citronella works briefly and wears off fast, so candles and plant-oil sprays are no substitute on a dengue day.

Most visitors don't. NaTHNaC says there's no malaria risk in Bangkok, Chiang Mai, Chiang Rai, Koh Phangan, Koh Samui or Pattaya, and the CDC lists no transmission on Krabi's islands, Koh Lanta, Koh Phi Phi and the Koh Yao pair included. Across most of the rest of the country the risk is rated very low, and the advice is bite avoidance, not tablets.

The exception is the rural, forested country along the borders, and here the American and British advice part ways. The CDC recommends prescription antimalarials for travelers to the provinces that border Myanmar, Cambodia and Malaysia. NaTHNaC rates the forested borders with Cambodia, Laos and Myanmar as low risk and says tablets may be considered only in exceptional circumstances, naming atovaquone with proguanil, or doxycycline, as the suitable ones. If your route includes border trekking or forest stays, see a travel clinic a few weeks before you fly and let them decide.

Dengue has no tablet and no routine traveler's vaccine, so on nearly every trip avoiding bites is the whole defense.

Dengue symptoms usually begin 4 to 10 days after the bite and last 2 to 7 days. The World Health Organization's list is a high fever, a severe headache, pain behind the eyes, muscle and joint pain, nausea and a rash. If that's you, go to a private hospital for a blood test, which costs a few hundred baht.

Take paracetamol, which Americans know as acetaminophen, for the fever and pain. The WHO says ibuprofen and aspirin should be avoided with dengue. The dangerous stage often comes after the fever has gone, so severe stomach pain, vomiting that won't stop, bleeding gums or a nosebleed, fast breathing or feeling very weak at that point means going straight back to the hospital.

Most cases pass with rest and fluids, and some need a few nights on a drip. A dengue admission to a private ward runs ฿50,000 to ฿150,000, which is the practical reason to have travel insurance sorted before the first bite.