Can Hot, Humid Nights Make Sleep Apnoea Worse?

Possibly, but the evidence pulls in two directions. The largest datasets, built from more than 100,000 under-mattress sensors, link hotter days with more breathing interruptions the following night. A controlled sleep lab trial found the opposite: people with sleep apnoea had fewer events in a warm room than a cool one. Humidity is murkier still. If you snore, gasp or wake up unrefreshed, hot weather is a reason to get checked, not a diagnosis.

Why hot nights and breathing deserve a closer look

Nights are warming too. A Nature commentary in August 2026 noted an overnight minimum of 32.4°C in Delhi in May and a record overnight low of 22°C in France in June. In Singapore, warm, humid nights aren't a heatwave. They're the baseline, so the question matters all year.

Obstructive sleep apnoea (OSA) is when the upper airway partly or fully collapses during sleep, over and over. Doctors count these events per hour of sleep as the apnoea-hypopnoea index, or AHI. An AHI of 15 or more is usually called moderate to severe.

It's also common. The Singapore Health Study 2012 ran home sleep tests on 242 adults and estimated that 30.5% of the adult population had an AHI of at least 15. Of those, 91% had never been diagnosed. The authors of the biggest heat study below put global OSA at close to a billion adults, with roughly 80% undiagnosed or untreated.

What the big sensor studies found

In 2025, a team at Flinders University in Australia published an analysis in Nature Communications of 116,620 people who used an FDA-cleared under-mattress sleep sensor, covering about 62 million nights across 41 countries over three and a half years. Each night was matched to local weather.

On the hottest days (a 24-hour average of 27.3°C, the 99th percentile in their data) compared with cooler days (6.4°C, the 25th percentile), the probability of a night with an AHI of 15 or more was 45% higher. For severe OSA it was 49% higher. The link held in 29 of 41 countries, strongest in Europe, after adjusting for humidity, pollution and other weather.

A companion study in Communications Medicine followed 70,052 people with an average AHI of 5 or more. Moving from a 6°C to an 18°C day was associated with a 6.4% rise in AHI. For sticky climates, the notable bit: they found no association between outdoor relative humidity and AHI. The authors say the physiology behind the seasonal pattern still needs to be worked out.

Caveats for the larger study: users were mostly men (22.7% women) living mainly in highly developed countries, there was no indoor temperature data, and one author consults for the sensor maker.

What the sleep lab found

A randomised trial in Umeå, Sweden, went the other way. Forty untreated patients with mild to moderate OSA (AHI 10 to 30) slept three nights in hospital rooms set to 16°C, 20°C and 24°C, measured by full polysomnography.

The obstructive AHI was 30 at 16°C, 28 at 20°C and 24 at 24°C. So the warm room had fewer breathing events. Yet in the cool room, people slept about 30 minutes longer, had higher sleep efficiency (77% vs 71%) and felt more alert the next morning. Time in each sleep stage didn't change.

A decade of lab records from Porto Alegre, Brazil, agrees. Across 7,523 patients, AHI peaked in winter (median 17.8 events per hour in colder months vs 15.0 in warmer ones), falling with temperature but rising with relative humidity.

And what about humidity?

Two large sleep centre studies from Taipei, Taiwan, looked at humidity directly. In 5,204 adults, higher relative humidity was associated with a higher AHI, more time sleeping on the back and more events while on the back, while higher temperature was linked to a lower AHI. In a second group of 8,628 people, each 1% rise in humidity was associated with only 0.01 to 0.03 extra events per hour, with the clearest pattern in the cold season.

The evidence at a glance

| Study | Who and where | Heat and apnoea | Humidity and apnoea | |---|---|---|---| | Lechat 2025, Nat Commun | 116,620 sensor users, 41 countries | Hottest vs cool days: 45% higher probability of an AHI 15+ night | Adjusted for, not the focus | | Lechat 2025, Commun Med | 70,052 sensor users with AHI 5+ | 6°C to 18°C: AHI up 6.4% | No association | | Valham 2012, Sleep | 40 patients, Sweden, lab | AHI lower at 24°C than 16°C, but sleep worse | Not tested | | Cassol 2012, Chest | 7,523 patients, Brazil | AHI higher in winter | Higher humidity, higher AHI | | Liu 2022 and Bai 2023 | 5,204 and 8,628 patients, Taiwan | Warmer linked to lower AHI (Liu) | Higher humidity, slightly higher AHI |

Why the studies disagree

The sensor studies used outdoor weather, not bedroom air, and compared each person's own nights. The clinic studies compared different patients across seasons, or one night per room. None tested a 28°C humid bedroom or aircon at 25°C, which is how many people in Singapore actually sleep.

Heat also changes sleep itself. As the Swedish trial showed, fewer events and better sleep aren't the same thing.

What this means on a sticky night

None of this diagnoses anything, but a few habits make sense:

1. Notice patterns. If a partner notices louder snoring or pauses on hot nights, note it for your doctor.
2. Keep the bedroom comfortable and steady. Our pieces on bedroom heat and sleep efficiency and fans in humid heat cover the basics of humid night sleep.
3. Mind your sleep position if you've been told it matters. The Taiwan data linked humid stretches with more back sleeping. It's observational, but relevant if your events cluster on your back.
4. Check before adding weight on top. In a small study of 26 people with insomnia, a weighted blanket at about 10% of body weight improved several sleep measures over 10 nights, but obstructive AHI also rose. The authors recommended screening for sleep apnoea first. If you have or suspect apnoea, ask your doctor before using any weighted blanket, including a cooling weighted blanket designed for hot climates. Our weighted blanket safety guide covers who else should skip one.

See a doctor if your breathing stops and starts during sleep, you make gasping or choking noises, you snore loudly or you always feel very tired during the day. In Singapore, a GP or polyclinic is a good first stop and can refer you for a sleep study if needed. Sleep apnoea can be serious if it isn't diagnosed and treated, and most cases are still missed.

Sources

1. Gong P, Lan L, Guo R, et al. Too hot to sleep? How heatwaves at night affect our health. Nature (Comment). 17 August 2026. https://www.nature.com/articles/d41586-026-02532-2
2. Lechat B, Manners J, Pinilla L, et al. Global warming may increase the burden of obstructive sleep apnea. Nature Communications. 2025;16:5100. https://doi.org/10.1038/s41467-025-60218-1
3. Lechat B, Nguyen DP, Sansom K, et al. Obstructive sleep apnea severity varies by season and environmental influences such as ambient temperature. Communications Medicine. 2025;5:314. https://doi.org/10.1038/s43856-025-01016-0
4. Valham F, Sahlin C, Stenlund H, Franklin KA. Ambient temperature and obstructive sleep apnea: effects on sleep, sleep apnea, and morning alertness. Sleep. 2012;35(4):513-517. https://doi.org/10.5665/sleep.1736
5. Cassol CM, Martinez D, da Silva FABS, et al. Is sleep apnea a winter disease? Meteorologic and sleep laboratory evidence collected over 1 decade. Chest. 2012;142(6):1499-1507. https://doi.org/10.1378/chest.11-0493
6. Liu WT, Wang YH, Chang LT, et al. The impacts of ambient relative humidity and temperature on supine position-related obstructive sleep apnea in adults. Environmental Science and Pollution Research. 2022;29(33):50755-50764. https://doi.org/10.1007/s11356-022-18922-8
7. Bai KJ, Liu WT, Lin YC, et al. Ambient relative humidity-dependent obstructive sleep apnea severity in cold season: a case-control study. Science of the Total Environment. 2023;861:160586. https://doi.org/10.1016/j.scitotenv.2022.160586
8. Tan A, Cheung YY, Yin J, et al. Prevalence of sleep-disordered breathing in a multiethnic Asian population in Singapore: a community-based study. Respirology. 2016;21(5):943-950. https://doi.org/10.1111/resp.12747
9. Benbir Şenel G, Karadeniz D. Interim analysis of a prospective polysomnographic study of weighted blankets in patients with psychophysiological insomnia. Psychiatry and Clinical Psychopharmacology. 2024;34(4):365-370. https://doi.org/10.5152/pcp.2024.23795
10. NHS. Sleep apnoea. https://www.nhs.uk/conditions/sleep-apnoea/