Expert warns people should never run fan all night in hot weather

An expert has revealed why you shouldn’t leave a fan running throughout the night during the heatwave, despite how appealing it may seem.

With temperatures climbing above 30 degrees across certain areas of the UK, Brits will be frantically seeking methods to stay cool. From adding ice to beverages to donning lighter garments, there are numerous tactics people will be employing. And one particularly common approach is keeping a fan operating day and night. However, experts have cautioned this may not be advisable.

Natalie Pennicotte-Collier, sleep therapist and resident sleep expert at MattressNextDay, cautioned that keeping one switched on throughout the night could actually compromise sleep quality.

Why should you not run your fan all night?

Natalie explained that while fans can help individuals drift off more quickly in warm conditions, they can regrettably begin disrupting sleep during the later hours as the body naturally adjusts its temperature before waking.

“What helps you fall asleep is not always what supports your best quality sleep across the whole night. A fan can ease sleep onset, but as the room cools further in the early hours and your core body temperature begins to change before waking, that same fan can start to fragment your sleep, triggering lighter waking as your body tries to regulate itself.”

She argued that many people presume staying cool throughout the night automatically guarantees better sleep, yet the body actually requires a slight rise in temperature before waking naturally. She said: “With a fan running all night, the constant airflow continues to cool and dry the air around you, which can interfere with that natural process.”

According to Natalie, this explains why some people repeatedly wake in the early hours or still feel drained the following morning despite having clocked up sufficient hours of sleep.

It can also aggravate your airways, drying them out considerably. “A fan running all night progressively dries the mucosal membranes lining your nose, throat and upper airways. Your body responds by producing more mucus,” she said.

She noted this can leave people waking with blocked noses, parched throats and disrupted sleep, without ever suspecting their fan could be the culprit.

Fans can also exacerbate hayfever symptoms, as you’re “essentially circulating primary triggers continuously in a closed bedroom for seven or eight hours,” which is far from ideal and may intensify suffering, causing itchy eyes first thing in the morning, despite appearing to have slept for ‘long enough’.

However, there are still measures you can take to continue enjoying the relief your fan provides during the night.

1. Set a timer

Natalie explained that people can still enjoy the cooling effects of a fan without subjecting themselves to hours of continuous airflow throughout the night. She advised: “Use your fan to cool the room before sleep, or set a timer so it switches off after an hour.”

This allows people to cool down sufficiently to drift off to sleep while avoiding the dryness and temperature disruption that can occur later during the night.

2. Don’t blow air directly into your face

Sleeping directly in the path of a fan can worsen airway dryness overnight, particularly affecting the nose, throat and eyes. She recommended you “point the fan towards the ceiling or a wall, not directly at your face or body, to reduce airway drying while still cooling the room”.

Natalie noted this still assists in circulating cooler air throughout the room without directing airflow straight onto the body for prolonged periods.

3. Clean your fan more often during a heatwave

Throughout the summer months, fans can rapidly accumulate dust, pollen and other particles, which are subsequently circulated around the bedroom overnight. She strongly encouraged people to clean fans “thoroughly and regularly” as “blades are one of the most effective dust collectors in your bedroom”.

Natalie stressed that this is particularly crucial for those suffering from hay fever, asthma or dust allergies.

4. Close windows when the pollen count is high

While many people throw open windows during sweltering weather, Natalie warned this can occasionally worsen nocturnal allergy symptoms. She advises keeping windows shut during the evening if pollen counts are especially elevated, particularly when running a fan in the bedroom, as fans can constantly recirculate allergens throughout the room overnight.

5. Drink more water when it’s warm

Maintaining proper hydration can help offset some of the drying effects triggered by overnight fan usage. “Stay well hydrated through the day and keep water by your bed. Counteracting the drying effect of fan use starts with good hydration,” she stressed.

She explained this can help people awaken with reduced throat dryness and discomfort the following morning, and you’ll likely sleep more soundly.

The NHS advises you drink six to eight cups of fluid per day if you’re an adult, and you can consume more if you’re dehydrated and perspiring heavily in the sunshine.