3. Dandruff
Dandruff can be caused by dry scalp, eczema, psoriasis, or a fungus, all of which can be exacerbated by sleeping with wet hair. (3)
Fungus thrives where it’s warm, dark, and moist—your scalp is all of the above when you go to bed with wet hair. Additionally, skin that is kept wet and left to slowly air-dry can worsen the itchiness and flaking caused by eczema and psoriasis.
4. Dullness
Shine comes from your hair’s moisture and natural scalp oils. When you place your wet head on a dry pillowcase, the fabric absorbs moisture from your hair and leave the hair shafts dehydrated and lackluster.
5. Ringworms
Scalp ringworm is a highly contagious fungal infection that itches terribly and can cause patchy hair loss. It’s called “ringworm” because it grows in red, scaly circles.
Scalp ringworm is a different strain than the ringworm that grows on other parts of the body or on the skin of your family pet. (4)
When you lie on a pillow with wet hair, the pillow becomes warm and damp; the combination of damp hair and damp pillow fosters fungal growth. It also makes you more likely to infect other family members, especially if you share a bed.
6. Bacteria and Mold
Just as in the case of fungi, bacteria and molds that normally reside on your scalp can grow out of control in a warm, damp environment. Bacteria and mold growth can cause a flaky scalp, which can lead to hair loss.
On top of that, making it a habit of sleeping with wet hair can cause these micro-organisms to penetrate into your pillow, where they can take up residence and cause reinfection. (5)