Dengue in Thailand: when the season is, how to avoid bites and what to do with a fever

Dengue (ไข้เลือดออก) in Thailand is mostly caught in the rainy season. Below: the season calendar, how to avoid bites in Phuket, Samui and other resort areas, the symptoms and the signs that mean you must not wait. The data was checked on 19 October 2026; the medical advice is general and does not replace a doctor.

When is dengue season

The Department of Disease Control (DDC) of the Ministry of Public Health describes a typical year like this: cases start rising in April, peak in June-August and decline in September. If many cases remain at the end of the year, outbreaks can continue into the next year. The rainy season on the west coast runs from May to October; see our guide to the low season in Phuket.

The table comes from the DDC release of 15 September 2026. It has no provincial data, so we give no separate figures for Phuket or Samui.

How dengue spreads

The virus is carried by female Aedes aegypti and Aedes albopictus mosquitoes, and dengue does not pass directly from person to person (DDC). WHO stresses that these mosquitoes are active in the daytime. The Government of Canada adds that they bite especially at sunrise and sunset. The same mosquitoes carry chikungunya and Zika, so protection against them works against three diseases.

A sick person is infectious to mosquitoes from 2 days before symptoms start to day 6 of the illness (DDC). If you fall ill, avoid bites so you do not pass the virus on.

How to protect yourself

• Daytime repellent: WHO names products with DEET, picaridin and IR3535
• Clothing that covers as much of the body as possible; the DDC advises long sleeves and long trousers
• Nets: mosquito nets for daytime sleep and window screens (WHO), and in forests and the outdoors a net over a hammock (DDC)
• Standing water: remove containers that collect it, change vase water weekly and cover water tanks (DDC, WHO)
• Accommodation: check the balcony and plant saucers for standing water; this is our advice, drawn from the DDC rule on water containers

The DDC sums up home rules in the «3 Keeps» formula: clear rubbish and water containers, keep the house tidy and bright, and cover water. Repellents and nets are sold in pharmacies; see our guide to pharmacies in Thailand.

On malaria: the CDC advises preventive tablets only for provinces on the borders with Myanmar, Cambodia and Malaysia, and bite avoidance elsewhere. For what else the CDC advises see our guide to vaccinations.

What dengue symptoms look like

Symptoms start 4-10 days after a bite and last 2-7 days (WHO). The DDC gives a wider incubation of 3-14 days, most often 4-7. Typical signs per WHO:

• High fever
• Severe headache and pain behind the eyes
• Muscle and joint pain
• Nausea and vomiting
• Swollen glands
• Rash

Most people have a mild illness or no symptoms and recover within 1-2 weeks (WHO). Dengue cannot be diagnosed from symptoms alone and needs a test, so with a fever go to a hospital or clinic.

When to see a doctor urgently

The DDC lists signs that mean going back to a doctor immediately:

• The fever has gone but you feel worse, very weak, restless or agitated
• Abdominal pain, or vomiting more than 3 times a day
• Dizziness, fainting, cold hands and feet, drowsiness
• Little or no urine for 4-6 hours
• Abnormal bleeding: nosebleeds, black stools, vomiting blood, heavy periods, dark brown or black urine

WHO adds rapid breathing, bleeding gums and blood in vomit or stool. If the fever does not fall within 1-2 days after a fever reducer or sponging, see a doctor right away (DDC). The DDC also writes that a doctor usually monitors patients from day 3 of fever and daily until they have been fever-free for at least 24 hours without fever reducers, so expect follow-up visits. In a life-threatening situation call 1669; for information about the disease the DDC line is 1422.

What to take for a fever

The DDC and WHO agree:

• Paracetamol for fever and pain, with the dose taken from the leaflet or a doctor’s advice
• Do not take ibuprofen, diclofenac, aspirin or other NSAIDs: they raise the risk of bleeding, and the DDC rules them out
• Do not pick medicines yourself: the DDC asks people not to buy them without advice
• Drink plenty of fluids: the DDC prefers oral rehydration solution or juice to plain water

At the pharmacy say plainly that you suspect dengue and ask whether the product contains an NSAID. That is our advice, drawn from the DDC ban. How to find an equivalent of your medicine is in our guide to pharmacies.

If you fall ill on a trip

Private hospitals treat on a payment guarantee from your insurer: the UK Foreign Office writes that all hospitals require a guarantee of payment before treatment, so you need a policy before travelling; see our guide to insurance. A list of hospitals with interpreters and phone numbers is in hospitals in Phuket. All the numbers are on the page emergency numbers in Thailand.

Found an error or outdated fact? Tell the editors, we will fix it and update the check date.