Despite the rise of the no-shampoo movement, there's always been one thing that stops me from going any more than three days without washing my hair: the smell.After my hair has absorbed the oils, city grime, and sweat of the past three days, a quick spritz of dry shampoo feels more like a Febreze cover-up than a laundry day. And unfortunately, it's not all that effective."The hair and scalp end up smelling because there's a build-up of sebum and sweat, and it makes it a breeding ground for yeast, dead skin cells, and bacteria," dermatologist Francesca Fusco , MD, says.In fact, sweat itself doesn't have an odor — bacteria (or the byproducts of bacteria) does, and it will feed off lipids and proteins in your sweat, secreting compounds that smell like onions or cheese . Your scalp, it turns out, is just like the rest of your body — it sweats, with oils and fatty acids, and then bacteria sets in to feast.But why does hair smell more than, say, your face? "Yes, when you don't wash your face, your face doesn't smell so bad, but your scalp does," Dr. Fusco says. "Your hair keeps your scalp warm, and it's a little incubator for all that bacteria." Gross.That said, having smelly hair isn't a sign of poor hygiene. "Some people are just really oily, and they need to shampoo every day," Dr. Fusco says. But, contrary to popular opinion, you can't train your hair to be less oily. "That's all hormonal. Putting something on the surface of the skin is not going to tell those oil glands to stop pumping," she says. "You could dry it out too much, get irritated, and make it even more oily."There are a few remedies to help with hair smell, even if you are on day three or four. Dry shampoo will absorb some of the sweat and oil, and typically the fragrance will neutralize any unsavory scents. But it's not a permanent solution, and it can affect your scalp health if used in excess Instead of relying on sprays and powders, Dr. Fusco recommends one easy trick with a tool you already have: a hairdryer on the cool setting. When tasked with the idea of fending off bad hair smells post-Korean barbecue, Dr. Fusco recommends blasting your hair with cold air to aerate the area — the same way a brisk breeze will freshen up a room. "I personally have thick, curly hair, and it takes up fragrance," Dr. Fusco says, "so I use that thing that cleans your keyboard out, and blast it around to aerate it."Preventative treatments can also help. Dandruff shampoos are particularly good at keeping your scalp healthy, since they help monitor your oil production. "[Dandruff is] caused by a lipophilic yeast, which means that it eats oil," David Kingsley , PhD, a trichologist in New York, tells Refinery29 . The zinc pyrithione used to treat dandruff essentially kills off the yeast that causes the annoying white flakes, Dr. Fusco says.For a more permanent solution, there is also the option of Botox, which will last for three to six months. "Some people do get Botox injected into their scalp to reduce sweating, and that will reduce a smelly scalp," Dr. Fusco says, much like how Botox injected into armpits will stop sweating there . "So it's out there, and some people do it."But if you want options that don't require a trip to the derm and won't hurt your bank account, click through the slides ahead for three beauty buys that will keep smelly hair at bay.