How to Stay Healthy and Ready for the Changes in the Weather

Last updated 14 July 2026

The first heavy rain of the season has a smell. Warm tar, the drain behind the shophouse, the drop in pressure a minute before the water comes down. By late November the whole country is checking the sky the way other places check a calendar.

Malaysia does not have four seasons. It has weather events. Each one carries its own health risk, on a fairly predictable schedule. Knowing which risk belongs to which event is most of the work.

Malaysia’s weather year, in plain terms

The Malaysian Meteorological Department describes two monsoon regimes. The Southwest Monsoon runs from late May to September. The Northeast Monsoon runs from November to March. The Northeast Monsoon is the main rainy season. MetMalaysia notes it brings the heavy rain that often causes large floods in Kelantan, Terengganu, Pahang and east Johor, as well as Sarawak and Sabah. Between them sit the inter-monsoon periods, roughly April to May and October to November. That is when thunderstorms are most frequent.

So the health year has a shape: floods, then mosquitoes, then haze, with heat throughout. Most of it is infectious disease, and nearly all of it is preventable.

1. The monsoon and floods

Floodwater is not rainwater. It is drain water, sewage, soil, fuel and rubbish, moving. It carries infection, chemical hazards and injury risk at once. And the infection it carries best here has a name most people only half recognise.

Leptospirosis: the one to take seriously

Leptospirosis is caused by Leptospira bacteria. They are carried in the kidneys of rats and other animals, and shed in their urine. The Ministry of Health’s national guidelines on leptospirosis are published by the Disease Control Division. They describe infection being acquired through the skin, or through the membranes of the eyes, nose and mouth. It happens on contact with water or soil contaminated by that urine. Swallowing it will also do it. Flooding and blocked drains are named directly as risk factors. Water logging drives rodents out of their burrows, and into the stagnant water everyone is wading through. A small cut on the foot is a textbook exposure.

The incubation period is usually about 10 days. It can run anywhere from 2 to 30 days. The ministry’s case description lists fever with headache, muscle pain especially in the calves, joint pain, red irritated eyes, jaundice, rash, and stomach symptoms such as nausea and vomiting. In its severe form, Weil’s syndrome, it causes jaundice, kidney failure, bleeding and damage to the heart muscle. The illness is classically biphasic. That means a patient can seem to be recovering, and then deteriorate.

Now the good news. Early antibiotic treatment is essential, and the ministry says so in exactly those words. Its National Antimicrobial Guideline recommends starting antibiotics when leptospirosis is suspected after a high-risk exposure such as a flood. It uses doxycycline for mild disease, and penicillin for severe disease. The trouble is that leptospirosis is known in the guideline as “the Great Mimicker”. And the disease it is most often mistaken for here is dengue.

	Leptospirosis	Dengue
Cause	Bacteria, from animal urine in water or soil	Virus, from an Aedes mosquito bite
Exposure	Wading in floodwater, drains, mud	Bites near water standing in containers
Pointers	Red eyes, jaundice, severe calf pain	Pain behind the eyes, rash, bone pain
Treatment	Antibiotics, the earlier the better	No specific medicine; supportive care

You cannot tell these apart at home. So if you develop a fever within a month of wading in floodwater, go to a clinic and say those exact words: “I walked through floodwater.” That sentence changes what the doctor tests for.

Water, food and wounds

Floodwater may contain sewage. So anything it has touched can carry the same faecal-oral infections that give us typhoid and hepatitis A. Boil your drinking water, and throw away food the water has reached. This is no moment for raw or lightly washed food. The water you would rinse it in may be the problem.

For the skin, the ministry’s leptospirosis guidance is easy to follow. Anyone exposed to contaminated water or soil should wear rubber boots and gloves. They should cover skin lesions with waterproof dressings. They should wash with clean water immediately after exposure, and get treatment early if symptoms appear. Floodwater also hides glass and metal. If you are cut, especially a puncture wound dirtied with soil, ask a health professional about a tetanus booster.

Melioidosis

Melioidosis comes from a soil and water bacterium, Burkholderia pseudomallei. The Ministry of Health’s MyHEALTH portal describes it as especially prevalent in Southeast Asia. It lives in stagnant water and wet soil such as padi fields. It infects people through broken skin, or by inhaling contaminated dust or droplets. It commonly presents as a lung infection, and treatment is long.

It matters here because of who it targets. MyHEALTH lists the main risk factors: diabetes, kidney disease, liver disease, thalassaemia, chronic lung disease and cancer. And diabetes is common in Malaysia. A study of 145 confirmed cases at Hospital Sultanah Bahiyah in Alor Setar was published in BMC Infectious Diseases. It found diabetes in 57 percent of patients, and both cases and deaths tracked monthly rainfall. Diabetes reaches well beyond blood sugar. That is one more reason to understand how diabetes raises your risk elsewhere in the body. The ministry’s advice is short. If you have diabetes or kidney disease and an open wound, stay out of contaminated soil and water. And if you work the land, wear boots and gloves.

Floods harm people in blunter ways too. Do not drive or walk through moving water; it is stronger and deeper than it looks. Treat submerged sockets and appliances as live until the power is off. Snakes get displaced by rising water. Never run a generator indoors.

2. Dengue comes after the rain, not during it

Aedes mosquitoes lay their eggs in containers holding water, and they live close to people. A storm fills every one of them: the pail, the saucer under the plant, the clogged gutter, the old tyre. The eggs then need time to become biting adults. So the dangerous moment is not the downpour. It is the still, sunny week or two afterwards. Everything is quietly full of water, and nobody is thinking about rain. That is when to walk round the house and tip it all out. The government’s iDengue portal is run by the Malaysian Space Agency with the Ministry of Health. It maps active outbreak localities daily.

One correction worth making. Aedes bites in the daytime, most actively in the early morning and late afternoon. That is why the ministry’s dengue guideline tells patients to use repellent or a mosquito net even during the day. The idea that mosquitoes are a dusk-and-night problem comes from malaria, which is carried by a different mosquito. And it leaves people unprotected all afternoon.

The fact that saves lives: dengue turns dangerous as the fever falls

Malaysia has its own clinical practice guidelines for dengue, on the Ministry of Health’s infectious disease guidelines page. They are Management of Dengue Infection in Adults, now in its third edition, and Management of Dengue in Children, in its second. Both are built around one idea. It is the most useful thing in this article.

The illness has three phases. First comes a febrile phase of high fever, lasting two to seven days. Then comes what the guideline calls the critical phase. It usually begins after the third day of fever, or around defervescence, the moment the temperature drops sharply. And here is the sentence that matters, close to the guideline’s own words. In other viral infections the patient improves as the temperature subsides. But in severe dengue the opposite happens, and the patient may deteriorate. The critical phase lasts about 24 to 48 hours.

This is what catches families out. The fever breaks, the family relaxes, and everyone assumes the worst has passed. But that is exactly the window when plasma leaks out of the blood vessels, and a patient can slide into shock. Nobody should be left alone during it. And nobody should stop watching just because the thermometer looks better.

The guideline’s warning signs are abdominal pain or tenderness, persistent vomiting or diarrhoea, restlessness or a change in consciousness, fluid accumulation, bleeding from the mucous membranes, and a tender liver. The version written for patients and families is blunter. Go straight to the nearest hospital or emergency department if you see:

• Bleeding: red spots or patches on the skin, bleeding from the nose or gums, vomiting blood, black stools, or unusually heavy vaginal bleeding.
• Frequent vomiting or diarrhoea.
• Abdominal pain or tenderness.
• Drowsiness or irritability.
• Pale, cold or clammy skin.
• Difficulty breathing.

Paracetamol, not ibuprofen

If dengue is suspected, the Malaysian guideline tells patients to take paracetamol for fever, and not more than 4 grams a day. Its home care advice then lists what to avoid. The first item is unambiguous: do not take non-steroidal anti-inflammatory drugs (NSAIDs), for example aspirin or mefenamic acid, or steroids. If you are already on them, speak to your doctor. The same caution covers ibuprofen and diclofenac. These drugs affect bleeding and irritate the stomach. And bleeding is part of what makes severe dengue dangerous. The guideline also tells patients not to take antibiotics, which do nothing against a virus. It also tells them not to have injections, massage, cupping or gua sha while infected.

3. Haze

Air quality here is reported as the Air Pollutant Index, or API. It is published by the Department of Environment. It is calculated from five pollutants: sulphur dioxide, nitrogen dioxide, carbon monoxide, particulate matter under 10 microns, and ground-level ozone. Live readings are at the department’s air quality portal. The bands below, and the health advice attached to each, are the department’s own.

API	Status	Official health advice
0 to 50	Good	No restriction on outdoor activities
51 to 100	Moderate	No restriction on outdoor activities
101 to 200	Unhealthy	High risk people limit outdoor activity; public reduce strenuous outdoor activity
201 to 300	Very unhealthy	Elderly and high risk people stay indoors, reduce activity; see a doctor if unwell
Above 300	Hazardous	Elderly and high risk people should not go outdoors; public avoid outdoor activity
Above 500	Emergency	Follow National Security Council orders and announcements

The Department of Environment defines the high risk group as elderly people and those with heart and lung complications. In practice, that means anyone with asthma, chronic obstructive pulmonary disease or heart disease. Sensibly, it means young children and pregnant women too. If you have asthma, check before haze season that your reliever inhaler is in date.

What helps: staying indoors with windows shut, running a HEPA air purifier in the room you use most, and skipping outdoor exercise. Hard breathing drives more particles deep into the lungs. If you must be out, a properly fitted N95 respirator filters at least 95 percent of airborne particles, and seals against the face. A loose surgical or cloth mask does neither.

A cough during haze is not automatically the haze. Respiratory infections circulate here all year. So it is worth knowing why flu cases have been rising.

4. Heat

The Ministry of Health’s MyHEALTH portal sets out heat-related illness as a ladder. It runs from heat cramps and heat syncope up to heat exhaustion and, at the top, heat stroke.

Heat exhaustion is what happens when the body loses too much water and salt. It is typically seen in older people, and in those working in the heat without enough fluid replacement. The portal lists nausea, vomiting, headache, lethargy and dizziness. The temperature is normal or raised, but still below 40 degrees Celsius, and blood pressure drops on standing. Move the person somewhere cool, give cool water in sips, and get them assessed.

Heat stroke is a medical emergency. MyHEALTH defines it as a life-threatening illness. The core body temperature rises above 40 degrees Celsius, and the nervous system stops working properly. That produces inappropriate behaviour, confusion, delirium, unsteadiness, seizures or coma. It is often fatal if left untreated.

One detail deserves to be read twice. The ministry lists the skin as either “sweating or no sweating”. People assume heavy sweating rules out heat stroke. It does not, and the assumption costs time. Does someone in the heat become confused, stop making sense, or collapse? Call 999. Move them out of the heat, remove excess clothing, spray or sponge them with cool water, and fan them. Place ice packs at the neck, armpits and groin. Do not give paracetamol or aspirin. The portal is explicit that they have no role in heat stroke, and may make things worse. Most at risk are outdoor workers, athletes, older adults, and children, including the ones left in parked cars.

Hydration, done properly

Forget the eight glasses rule. It is not a medical guideline and never was. Drink when you are thirsty, and drink noticeably more when active, sweating or working in heat. One exception matters. People with kidney failure, heart failure or certain other conditions may be on a deliberate fluid restriction. For them, “just drink more water” is not harmless advice. Follow your doctor’s instructions. And if you are unsure how your kidneys are doing, start with what everyone should know about caring for their kidneys.

5. What to actually do

Know before it arrives. MetMalaysia issues warnings for continuous rain, thunderstorms, and strong wind and rough seas. They are on its website and the myCuaca app. The National Disaster Management Agency, NADMA, coordinates the national response. It publishes evacuation information at nadma.gov.my. Follow both before the monsoon, not on the night the water rises.

Keep a small kit ready. Torch, power bank, drinking water, a first aid kit with waterproof plasters, documents in a sealed bag, and boots. Boots are the difference between wading and being exposed.

And do not forget your medication.

• On dialysis: ask your centre now what happens if it floods or loses power, and which backup centre to go to. Missing sessions is dangerous. Write the address and number on paper.
• On insulin: plan how you will keep it cool through a multi-day power cut, and store it where water will not reach it.
• Anyone on regular medication: keep a written list of your medicines and doses in your bag. At a relief centre, that list is what lets a stranger treat you safely.

None of this asks for a change of lifestyle. It asks for ten minutes a week emptying containers, boots instead of slippers, and one sentence at the clinic: “I walked through floodwater.”