Lung experts warn that using electric fans overnight can circulate dust and pollen and worsen some patients’ asthma symptoms.

On its website, the Children’s Hospital of Philadelphia noted that electric fans and open windows can increase the pollen count in your room, which could lead to more asthma problems at night.

If you have fans going all night long, allergens that cause symptoms get swirled around in the air before you eventually breathe them in, which makes the inflammation worse.

“No matter how clean and tidy you keep your room, there is always sneaky dust particles or pollen insistent on sticking around. This dust and pollen can attach itself to the fan blades which will circulate the air once switched on,” the London Allergy & Immunology Centre explained on its blog.