Lather, rinse, repeat—daily? Not necessarily. More women are stretching the time between one shampoo session and the next (especially as we’re in an extended WFH situation where you don’t really have to be around people).  “I definitely think there is a non-washing movement right now,” says Angela Lamb, MD, director of dermatology and an assistant professor at Mount Sinai Health System in New York City. In other words, if you’re wondering what happens if you don’t wash your hair, you’re not alone.

But fewer suds aren’t actually a new trend; they’re a return to how often our foremothers probably washed up. “Hundreds of years ago, people didn’t wash their hair the way they do now,” says Dr. Lamb. “And some people believe that washing daily may actually strip hair of its natural oil protectants.”

“Hundreds of years ago, people didn’t wash their hair the way they do now.”

But if an every-other-day routine might be healthier for your head, what about putting the kibosh on shampoo for three days? Or more? “There are so many variables to consider, from hair texture to hormones, your exercise routine to genetics,” says Dr. Lamb. Still, it’s possible to make some generalizations, she adds.

Here’s what happens if you don’t wash your hair

One day: Skipping one day of suds is unlikely to have any negative effects—and less frequent shampooing may actually leave your head feeling healthier. “Traditional shampoos have emulsifying agents that are powerful detergents,” explains Dr. Lamb. Daily use may cause scalp irritation or even allergic reactions, and over-cleansing will prompt the oil glands on your scalp to compensate by ramping up production. Leave your scalp alone, and that oil may make your hair appear shinier and healthier.

Three days: If you don’t usually go this long between hair washes, you’re probably starting to feel a bit ick. Especially for people with finer, straighter hair, the accumulated dirt, oil, and hair products will start to make your strands look visibly grimy and shiny. The exception: Women with coarse or curly textures can easily push to 10 days before that build-up is visible.

One week: After seven days out of your usual routine, your scalp may start to stink (think subtle whiffs of sour milk when you turn your head). That’s because hair naturally traps moisture against your scalp. All of those natural oils and post-exercise sweat is like a buffet for the bacteria we all have living on our scalps. More food means more bacteria—and a slightly odorous head of hair.

Your nose isn’t the only organ that will feel the difference of a week without washing, though. “Because the overlapping skin cells on your scalp aren’t getting a chance to be exfoliated, it causes this dry, itchy feeling,” says Dr. Lamb. And while it’s not bad for your health, it may be hard to resist raking your hands through your hair to indulge the itch.

One month: Again, every person’s hair is different—and if you’re using conditioner (which tends to have a mild cleansing effect), you can go a month or more without shampoo. But if you hit the one-month mark rinsing with nothing but water, you may find your hair is begging for help. “Bacteria can get trapped in the hair follicle more easily by this point,” says Dr. Lamb. That causes folliculitis, or an infection of the hair follicle. Other possible maladies include ingrown hairs from lack of exfoliation or seborrhoeic dermatitis, a severe type of dandruff marked by patchy redness and frequent itching.

Still, it is possible to give the shampoo bottle the boot for good, and many no-wash devotees talk of a “breakthrough” that happens when slimy, grimy hair seems to get used to its unwashed state and start looking fuller, shinier, and healthier. “At some point, your scalp readjusts,” says Dr. Lamb. But what works for your BFF may not work for you, so take a cue from your own noggin. “There’s no universal truth,” Dr. Lamb adds. In other words, you do your ‘do.

If you do develop scalp flakes, here’s a dermatologist’s recommendations for how to deal:

Here’s what happens when you use dry shampoo frequently. And before you wash again, don’t miss the best shampoos and conditioners for every hair type.

This story was originally published on October 3, 2017; it was updated on March 26, 2020.