A COOL bedroom can be a welcome escape from Malaysia's heat, especially at times like this.
However, it has been claimed that sleeping with the air-conditioning on all night can leave a person dehydrated by morning.
Is it true that a night under the air-conditioning could cause dehydration?
Verdict:
TRUE, BUT
Air conditioning may contribute to dehydration by reducing the humidity of the air, which can increase the amount of water the body loses through breathing and the skin.
Dehydration occurs when the body loses more fluid than it takes in.
It is more commonly linked to illness, diarrhoea, vomiting, heavy sweating, fever, alcohol use and insufficient drinking.
Still, a dry bedroom may add a small overnight drain on the body's water supply.
A 2025 peer-reviewed study of healthy adults in southern China found that people exposed to air-conditioned rooms with lower humidity had changes consistent with mild fluid loss and a modest decline in estimated kidney filtration rate.
The study compared air-conditioned environments with rooms cooled using electric fans.
The researchers found that lower humidity was associated with increased thirst and accelerated body-water loss.
However, the research did not establish that sleeping in air conditioning alone causes clinically significant dehydration.
It also did not measure direct hydration markers such as urine or blood osmolality.
A dry mouth, chapped lips, a scratchy throat or irritated eyes after a night with the air-conditioning on may therefore be signs that the room is dry, rather than proof of dehydration.
The National Health Service lists thirst, dark yellow and strong-smelling urine, urinating less often, tiredness, dizziness and a dry mouth, lips or tongue among the possible signs of dehydration.
Older adults, young children and people who are unwell can be more vulnerable because they may lose fluids more easily or may not drink enough.
The World Health Organisation advises drinking water regularly in hot weather and suggests setting air conditioning to 27°C while using an electric fan for added comfort.
There is no need to turn the bedroom into a tropical rainforest, but staying hydrated during the day and avoiding an excessively cold, dry room may make for a more comfortable night.
Sources:
https://pmc.ncbi.nlm.nih.gov/
https://www.who.int/news-room/
https://www.nhs.uk/conditions/
