With the on-going heatwave, particularly in the United Kingdom, many of us are dependent on electric fans and ceiling fans to cool off through hot nights. But some people could unknowingly face adverse health effects if the fan is too close or not clean enough.

Keep in mind that fans are beneficial in most cases, not just for relief from heat but also for improved sleep quality. Cool air, be it from an open window or an electric fan, can help people breathe better unless the air is very dry, said Dr. Michael Benninger from the Head and Neck Institute at the Cleveland Clinic, Ohio.

One of the benefits of fans is that they produce white noise, or a "humming" sound at a favorable frequency, which helps people fall asleep. "I suggest facing the fan away. It will still circulate the air while producing background noise," he added.

If you find yourself waking up with sore muscles often, you could have another reason to avoid having the fan too close while sleeping. According to Sleep Advisor, stiffness and soreness can occur because the concentration of cool air on a specific part of the body can make muscles tense up and cramp.

"This problem is especially common for people who sleep with it near their face and neck. If you’ve been waking up with a stiff neck in the morning, it might be because of the constant breeze," the website explained. 

And if not the inside of your body, the air could also affect you on the outside. People prone to dry skin may find their skin triggered (potentially in the form of acne breakouts) from the high and constant blast of air. For those with sensitive skin, using moisturizers or lotions can help.

Fans can also collect dust and dust mites easily, noticeably on their blades. If they are not cleaned enough, they can pose a health risk for people who suffer from allergies. When in use through the night, the fan can dispose and circulate the harmful particles around the room. 

The American Academy of Allergy, Asthma, and Immunology (AAAAI) states that dust mites are the most common allergy triggers. The academy recommends that vulnerable individuals regularly clean fans, rugs, and bedding regularly to avoid exposure to indoor allergens.

Overall, fans are safe to use when sleeping in most cases. People who wake up with dry skin, allergic reactions, or sore muscles are advised to look into alternatives or consider making changes in how they use the fans and how often they clean it. 

For other ways to deal with the heat at night, consider wearing lighter clothing, keeping enough water by your bedside, or taking a shower before sleeping.