Why you feel awful after sleeping with a fan on, according to experts

Many people who sleep with a fan running through the night complain of waking up feeling stiff and achy, or with a scratchy throat. But is fan-blown air actually bad for your health?

Experts say that for most adults, sleeping with a fan on can actually improve sleep. When a bedroom is too warm, the body cannot shed heat properly, leading to sweating that disrupts rest. Keeping the room cool with a fan helps people fall asleep faster and sleep more soundly.

Chester Wu, a psychiatrist and sleep medicine specialist, told Good Housekeeping that "sleep onset is triggered by a natural drop in body temperature." Research shows a cool room temperature — between 18 and 20 degrees Celsius — lowers body temperature and promotes more restful sleep. Wu added that a fan can also help prevent sleep disruption caused by excessive sweating.

The gentle hum of a fan can act as white noise, masking external sounds such as car horns or barking dogs. A 2021 study found that white noise improved sleep in people whose rest was disrupted by ambient noise.

The risks, however, depend on the cleanliness of the room and whether a person has allergies, asthma or dry eye syndrome. Purvi Parikh, an allergist at NYU Langone Health, told Good Housekeeping that people allergic to dust mites, pet dander or mold may find that a fan spreads these triggers around the room, causing a runny nose and sneezing.

Dry eye syndrome and sinusitis can also worsen. Direct airflow causes tears to evaporate quickly, leaving eyes dry and sometimes triggering a reflex overflow of tears. Dry, cool air in particular can dry out the nasal mucosa and thicken mucus, leading to congestion. Wu said indoor air circulation can dry out the skin, eyes and mouth, explaining that it works "on the same principle as the sore throat, nasal congestion and coughing people experience when using a ventilator."

Experts advise following a few basic rules to use a fan safely. Cleaning the fan regularly and running an air purifier alongside it can reduce exposure to allergens.

British sleep expert Martin Seeley advised checking whether the fan blades are free of dust if you experience frequent sneezing, watery eyes, a runny nose, a sore throat or difficulty breathing. "If possible, use an air purifier with a HEPA filter at the same time to minimize the spread of dust mites indoors," he said.

Pointing the fan toward a wall or the ceiling rather than directly at your face is also recommended, as it circulates air without blasting it at you. Setting a timer for two to three hours after falling asleep can also help, allowing the fan to switch off before body temperature changes in the night disrupt your comfort.