All hair care products deposit residue on your hair (this is a good thing; you want those nourishing ingredients to remain on the strands instead of swirling down the drain). However, that residue actually sits on the skin for quite some time: According to board-certified dermatologist Iris Rubin, M.D., founder of SEEN Hair Care, the residue from hair products travels down your face and body while you rinse, and it can transfer to your skin from your hair, towel, or pillow post-wash.
Specifically, her research suggests that residue from shampoo and conditioner can remain on the forehead, cheeks, scalp, and back for up to two hours. And for styling products (think leave-ins and curl creams), that residue remains for up to four. That’s a pretty big window for ingredients to seep into the skin and cause some unwanted irritation.
Perhaps it goes without saying: If your hair products contain iffy or pore-clogging ingredients, that two- to four-hour window can be a waving red flag for irritation.