Old wives’ tales warn that sleeping with wet hair can make you sick or increase your chances of catching a cold, but there isn’t any scientific evidence that it can directly cause respiratory illnesses. However, there are risks associated with sleeping with wet hair, including hair and scalp damage. And fungus is involved.
When you wake up in the morning after sleeping on wet hair, you may find your hair smelling like mildew, harboring a stale and damp aroma similar to the smell of the early stages of mold forming, said Dusty Schlabach, a hairstylist and owner of Thairapy Salon in South Pasadena, California.
“If the hair is wet, all these conditions contribute to a much slower drying process, and can create a perfect environment for fungus and bacteria to thrive,” Schlabach said. “If this happens often enough, it can grow into a real problem on the scalp causing yellow discoloration, itchiness, buildup and flakiness. All in all, it’s gross. With enough buildup, it even stinks. I see it on new clients all the time.”
Fungi flourish in dark, moist and humid environments, and can live on the dead tissue of hair, nails and outer skin layers. As a result, your pillow is a breeding ground for fungus to thrive. A 2005 study by Wythenshawe Hospital and the University of Manchester found that there can be up to 16 types of fungal species found on your pillow.
You might also wake up with broken and tangled strands that can be hard to recover to their healthy state, especially for people with curly hair.
“The outside layer of the hair, the cuticle, is meant to expand when wet, and contract as it dries,” Schlabach said. “If it stays stretched for too long, it can split and crack, compromising the health of that outer layer. It allows way too much penetration from water and products you might be using. This leads to dryness, which leads to brittleness, which leads to breakage, which visibly translates to stringy ends and frizz.”
In addition to hair breakage, we asked dermatologists about the types of fungal infections that can form in your hair, how your scalp is affected and what to do if you have to sleep with wet hair.