Common Wet Season Illnesses in Thailand and How to Protect Yourself

Thailand is a tropical paradise loved by many people around the world. But being a tropical paradise means it has wet seasons and the illnesses that follow such as Dengue Fever, Common Flu, Pneumonia, and more. Understanding the main causes of these illnesses can help you prevent them.

There are both pros and cons to traveling or living in Thailand during the wet season. Due to the lower number of tourists, it’s usually quieter, cooler, and calmer in most regions. The wet season, however, can also bring additional risks to your health, as mentioned.

In this Pacific Prime Thailand article, we look at the most common Thailand wet season illnesses to watch out for, and what you can do to avoid them.

When is the Wet Season in Thailand

The Land of Smiles has three official seasons: hot, cool, and wet. The wet season (in other words, Thailand’s flu season) begins around mid-May every year, and continues until mid-October when rainfall starts to become less frequent.

Dengue Fever

Thailand recorded between 45,145 and 158,000 dengue cases annually between 2022 and 2024. As of August 2025, Thailand had already reported more than 38,000 dengue cases and 37 deaths nationwide.

Dengue Fever usually causes body aches, fever, headache, and a skin rash with red spots. Worryingly, there’s around a 36 percent chance for this wet season illness to develop into Dengue Hemorrhagic Fever (DHF), which is associated with severe symptoms like:

Vomiting
Bruising
Uncontrolled bleeding
High fever
Diarrhea
Abdominal pain

Those with severe dengue fever must seek medical treatment immediately, as complications can be fatal and lead to circulatory system failure.

How to Protect Yourself From Dengue Fever

We actually discussed dengue fever prevention in one of our blog articles on dengue fever, but here’s a quick recap of the most important precautionary measures people living or traveling in Thailand should be aware of:

Get the dengue vaccine
Wear loose, long-sleeved clothing
Use an insect repellent
Remove water containers around your home
Consider purchasing an insecticide-treated bed net

Hand-foot-and-mouth Disease

As a contagious viral infection, hand-foot-and-mouth disease spreads through physical contact with the infected person’s bodily secretions. It is common among young children, with potential complications ranging from meningitis, encephalitis, paralysis, and more.

In most cases, the patient will suffer mild symptoms but will recover in several days. We recommend seeing a doctor if it keeps your child from drinking liquids. See below for a list of symptoms commonly associated with hand-foot-and-mouth disease:

Fever
Muscle aches
Painful red lesions on the inside of the mouth
Red rash on palms, soles, and occasionally the buttocks
Loss of appetite
Irritability in toddlers and infants

How to Protect Yourself From Hand-foot-and-mouth Disease

Avoid close contact with people infected with the disease and using their personal items. It’s also important to wash your hands frequently and only consume thoroughly cooked, steaming hot food.

Pneumonia

Another common disease in Thailand is Pneumonia, which is a wet season illness. Characterized by infection of one/both lungs, people with pneumonia usually experience physical symptoms such as shortage of breath, clammy skin, fever, chills, cough, and shaking.

Pneumonia can be a side effect of other health conditions – e.g. asthma. While most cases of pneumonia can be treated successfully, it can be fatal if left untreated, especially among young children, the elderly, and those with weakened immune systems.

How to Protect Yourself From Pneumonia

Maintaining good personal hygiene is also key as your hands are in constant contact with different types of bacteria, you should make it a habit to wash them with soap frequently and thoroughly to lower your risk of infection.

Pneumonia is highly contagious, so it is important that you try to keep others from getting infected as well. If you’re suffering from any of the above-mentioned symptoms, make sure you see a doctor as soon as possible.

Japanese Encephalitis

Like dengue fever, Japanese encephalitis is also a mosquito-borne illness that can, in severe cases, lead to inflammation of the brain.

While the risk of contracting this wet season illness is not very high when compared to the incidence rates of other illnesses such as dengue fever , you are at a higher risk if you live or travel to rural areas for a prolonged period of time.

In Thailand, the disease is more common in the northern region like Chiang Mai Valley.

People infected with Japanese encephalitis will usually develop the following symptoms:

Fever
Confusion
Vomiting
Headache
Difficulty moving

In severe cases, swelling can develop around the brain, and result in cognitive/neurological damage.

How to Protect Yourself from Japanese Encephalitis

The most effective ways of protecting yourself from Japanese encephalitis include preventing mosquito bites (e.g. by using an appropriate insect repellent), and getting the Japanese encephalitis vaccine at least 6 weeks before traveling to a high risk area.

Leptospirosis

Leptospirosis is a rare bacterial disease that affects both humans and animals. It’s spread through contact with soil, water, and food contaminated with the blood, urine, or tissue of an infected animal. The disease can be found in dogs, rodents, buffalos, and farm animals.

You’re more at risk if you spend a lot of time outdoors or work closely with animals. As such, certain occupations, such as farmers, veterinarians, are also more prone to contracting leptospirosis. In severe cases, patients may develop meningitis, kidney malfunction, or even death.

Common symptoms of leptospirosis include:

Fever
Headache
Skin rash
Jaundice (i.e. yellowing of your skin and eyes)
Muscle aches, especially on your legs
Vomiting

However, it’s interesting to note that some infected persons display no symptoms at all.

How to Protect Yourself From Leptospirosis

Avoid stepping on puddles as they may be contaminated by animal urine. It’s also a good idea to wear water repellent boots and wear long pants. Most importantly, avoid touching your eyes, ears, and mouth after coming into contact with contaminated substances.

Flu

Influenza remains one of the most common illnesses during Thailand’s rainy season. More than 373,000 influenza cases and 51 related deaths were reported between January and mid-June 2025 alone, highlighting the continued seasonal impact of the virus.

Thailand’s wet season also coincides with the country’s peak influenza season. Increased rainfall often leads to more time spent indoors and in crowded environments, which can increase the spread of respiratory viruses.

Common fly symptoms include:

Fever and chills
Coughing and sore throat
Body aches and headaches
Fatigue
Runny or blocked nose

While many people recover within several days, influenza can lead to more serious complications among young children, older adults, pregnant women, and individuals with underlying medical conditions such as asthma or chronic respiratory illnesses.

How to Protect Yourself from the Flu

The best form of protection against the flu is to stay healthy and boost your immunity. Regular exercise and a nutrient-rich diet are therefore key. The flu vaccine is also highly recommended, especially if you’re more at risk of developing medical complications arising from flu.

Malaria

Malaria remains a health concern in certain remote and forested areas of Thailand, particularly near some border regions. However, the risk is generally very low in major urban and tourist destinations such as Bangkok, Chiang Mai, and Pattaya.

The disease is transmitted through the bite of infected female Anopheles mosquitoes, which are more active during and after periods of heavy rainfall. The World Health Organization and CDC warn travelers to take necessary precautions before visiting forested or rural border provinces.

Common malaria symptoms include:

Fever and chills
Headaches
Fatigue
Muscle aches
Nausea and vomiting

Symptoms can appear between 7–30 days after infection and may initially resemble the flu. Severe malaria can become life-threatening without prompt medical treatment, particularly infections caused by Plasmodium falciparum.

How to Protect Yourself From Malaria

Travelers visiting higher-risk areas should speak with a healthcare provider about whether antimalarial medication is recommended before departure. Additional preventive measures include:

Using insect repellent containing DEET or picaridin
Wearing long-sleeved clothing and long pants outdoors
Sleeping under mosquito nets where appropriate
Staying in accommodations with screened windows or air conditioning
Avoiding outdoor mosquito exposure during evening and nighttime hours

Does Your Expat Health Insurance cover Wet Season Illness?

Medical treatment for wet season illnesses in Thailand can become expensive, particularly if hospitalization, specialist care, or emergency treatment at private hospitals is required. Ongoing monitoring and follow-up care will also add to the medical costs.

Having international health insurance can help provide financial protection and access to quality healthcare throughout Thailand. Depending on your policy, coverage may include:

Inpatient and outpatient treatment
Emergency medical care
Prescription medication
Vaccinations and preventive healthcare
Specialist consultations
International medical coverage
Maternity and family benefits
Dental and vision coverage

At Pacific Prime Thailand, we help expats, travelers, and businesses compare international health insurance plans from leading insurers. With over 25 years of experience, our team provides impartial advice and personalized support to help clients find coverage that fits their needs and budget.

Whether you are looking for individual health insurance, family coverage, corporate employee benefits, or travel medical protection, our advisors can help you compare plans and understand your options with confidence.

Contact Pacific Prime today for a free plan comparison and personalized insurance consultation.

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Vista Nip

Content Creator at Pacific Prime

Vista is a content creator at Pacific Prime. With over 8 years of writing experience for online platforms on various topics such as luxury lifestyle and digital entertainment. He enjoys diving into complex and otherwise confusing topics, and creating easy-to-understand content for the readers to help them navigate through the topic - something that’s perfectly aligned with Pacific Prime’s motto of ‘simplifying insurance’.

Born and raised in the cultural melting pot that is Hong Kong, and having studied at an international school, Vista has developed a multicultural perspective that he uses in his writing and strives to connect to people of different backgrounds.

In his free time, Vista enjoys immersing himself in different worlds, from video games to light novels and movies. His hobbies help him expand his writing style by putting himself in the point-of-view of different people and characters.