Most sleep experts put the best temperature for sleep at around 16 to 20°C, a range written for cool-climate bedrooms. In a Malaysian or Singaporean flat, a realistic target is a bedroom around 24 to 26°C with humidity kept in check, because what makes tropical nights hard is heat plus damp air, not heat alone.

If you've ever lain awake at 2am in a sticky tangle of bedsheet while the kipas siling clicks round uselessly, this one's for you.

Why does temperature affect sleep so much?

Your body temperature follows a daily rhythm. In the evening, blood vessels in your hands and feet widen to dump heat, your core temperature falls, and that drop is one of the signals that tells your brain it's time to sleep. Core temperature reaches its lowest point in the early morning hours.

When the room is too warm, that heat has nowhere to go. A 2012 review in the Journal of Physiological Anthropology by Okamoto-Mizuno and Mizuno concluded that heat exposure increases wakefulness and reduces both slow-wave (deep) sleep and REM sleep. The same review noted that humidity makes it worse: high humidity alongside heat further increased wakefulness, because sweat can't evaporate and cool you.

That's the tropical problem in one sentence. At 30°C and 50% humidity, sweat evaporates and does its job. At 28°C and 85% humidity, a typical monsoon-season night, it just sits on your skin.

Warm nights are also getting more common. A 2022 study in One Earth by Minor and colleagues, using sleep data from wearables in dozens of countries, estimated that hot nights are already costing people around 44 hours of sleep a year on average, with larger losses in warmer regions and among older adults.

What is the best temperature for sleep in a hot, humid country?

The widely quoted recommendation, including from the Sleep Foundation, is around 18°C (65°F), within a range of roughly 16–20°C. That's reasonable for London or Tokyo in winter. For most people in Southeast Asia, running aircon at 18°C all night is expensive, often uncomfortably cold, and dries out your skin and airways.

A more practical tropical approach:

• Room temperature around 24–26°C. Energy agencies in the region commonly recommend setting aircon at around 24–25°C, and with dry air and a light cover, most people sleep well there.
• Relative humidity around 40–60%. Drier air at 26°C often feels more comfortable than damp air at 24°C.
• Cool the room before bed, then ease off. Your body needs the biggest help in the first half of the night, when you're trying to fall asleep and getting most of your deep sleep.

There's no single perfect number. Age, body size, bedding and whether you share a bed all shift it. Use 24–26°C as a starting point and adjust by a degree at a time over a few nights.

Aircon, fan or both? A practical comparison

That last combination is underrated. Moving air makes you feel cooler at the same temperature, so a fan on low can let you set aircon a couple of degrees warmer with similar comfort and a smaller electricity bill.

Is it bad to sleep with the aircon on all night?

For healthy adults, not inherently. The main issues are practical:

• Dryness. Aircon removes moisture from the air, which can leave you with a dry throat, stuffy nose or tight skin. If you wake up parched, raise the temperature a notch and use a timer. Our guide to aircon and dry skin has more on protecting your barrier.
• Waking cold. Your body temperature is lowest in the early morning, so a setting that felt right at 11pm can feel freezing at 4am. A timer that switches off, or a slightly warmer setting after a few hours, solves this.
• Dirty filters. Dust and mould build up on filters in humid climates. Clean them regularly according to the manufacturer's instructions, especially if you have allergies or asthma.

The old warning that aircon "gives you a cold" isn't accurate; colds are caused by viruses. But dry airways can feel scratchy and uncomfortable.

How to sleep better on hot, humid nights: step by step

1. Pre-cool the room 30–60 minutes before bed with curtains drawn during the afternoon to block solar heat.
2. Take a warm shower 1–2 hours before bed. A 2019 meta-analysis in Sleep Medicine Reviews by Haghayegh and colleagues found that warm bathing (around 40–42.5°C) 1–2 hours before bedtime helped people fall asleep about 10 minutes faster on average. It works by drawing blood to the skin, which then speeds heat loss. In our climate, a warm rather than hot shower is enough.
3. Swap your bedding. Light cotton, linen or bamboo-derived fabrics breathe better than polyester. A thin blanket beats a thick duvet under full-blast aircon.
4. Keep your feet and hands free to release heat, unless your aircon is cold enough that you need socks.
5. Eat and drink with the night in mind. Heavy, late suppers and alcohol both disrupt temperature regulation and sleep. Alcohol also increases night-time waking.
6. Use the fan wisely. Aim it across the body rather than directly at your face.
7. Set a timer or schedule so the aircon warms up slightly in the early morning.

What if you don't have aircon?

Plenty of people don't, or prefer not to run it. Useful options:

• Create cross-ventilation by opening windows on opposite sides in the evening, when outdoor air is cooler.
• Place a bowl of ice in front of a fan for a short-term cooling boost.
• Sleep on the lowest floor available; heat rises.
• Cool your pulse points with a damp cloth before bed.
• Keep electronics and lights off, since they add heat.

If hot nights are regularly cutting into your sleep, the damage accumulates. We've written about why so many people in Southeast Asia sleep too little, and if your schedule has drifted too, see how to reset your sleep schedule.

This article is general information, not medical advice. If you have ongoing insomnia, loud snoring, or night sweats that aren't explained by room temperature, speak to a doctor, especially if you are pregnant, on medication or managing a health condition.

Frequently asked questions

What is the best aircon temperature for sleeping in Malaysia?

Around 24–26°C suits most people, especially combined with a fan and light bedding. Humidity matters too, so dry mode on muggy nights can make a warmer setting feel comfortable. Adjust by one degree at a time until you find what works for you.

Is 18°C too cold for sleeping?

Not in principle; it sits within the range many sleep organisations recommend. In practice, in tropical homes it often means high electricity costs, dry airways and waking cold in the early morning. Many people sleep just as well at a warmer setting with lower humidity and air movement.

Why do I sleep badly on humid nights even when it's not that hot?

Your body cools itself mainly by evaporating sweat, and humid air slows evaporation. Research on thermal environments and sleep has found that heat combined with high humidity increases wakefulness more than heat alone. Reducing humidity with dry mode, a dehumidifier or better ventilation often helps.

Is sleeping with a fan on bad for you?

For most people, no. Fans improve comfort by helping sweat evaporate. Some people find a fan blowing directly on their face dries their eyes, nose or throat, so angle it across the body and keep the blades clean to avoid spreading dust.

Does a cold shower before bed help you sleep?

A cold shower feels refreshing but can be stimulating, and your body may respond by conserving heat. Research supports warm showers or baths 1–2 hours before bed instead, as they bring blood to the skin and help your core temperature drop afterwards.

Sources

1. Sleep Foundation: Best temperature for sleep
2. NHS: Insomnia
3. CDC: Sleep
4. PubMed search: Okamoto-Mizuno and Mizuno (2012), effects of thermal environment on sleep and circadian rhythm
5. PubMed search: Haghayegh et al. (2019), warm bathing before bedtime meta-analysis
6. World Health Organization: Heat and health