Hair washing: A topic of controversy for virtually every woman, and even man, on Earth. How often, really, are you supposed to shampoo your hair?

If you ask your friends, you’ll probably get a different answer for the frequency in with washing occurs. Some people wash their hair every single day in order for them to feel good. Others take a break each day, and go for every other day without it cleaned. And some may even wash their hair just once a week, or even longer (e.g., they shower with a shower cap on).

On a PureWow segment called #TheGlowUp, Beauty Director Jenny Jin asked her fellow colleagues how often they washed their hair, and, as suspected, everyone’s answer was different. But no one really had quantitative reasons for why they washed their hair as often as they did. That’s just what they did!

So, is there a scientific answer for how often to wash your hair? Or does it depend on the person and their hair? To help answer the age-old question, celeb hairstylist and Co-Founder of Act and Acre, Helen Reavey, weighed in.

“What I tell people is, forget everything you were told about how to wash your hair—let’s restart again,” Reavey tells Jin.

She explained that there’s a common misunderstanding when it comes to washing your hair: that it’s not actually your hair that’s the most important part of hair care—it’s the scalp. Most specifically, it’s the nape of your neck that you should be paying attention to.

“Don’t wash your hair, wash your scalp,” Reavey clarifies.

On top of simply stating the facts about washing your hair, Reavey shows us up close and personal just what she’s talking about by using a microscopic camera to inspect Jin’s and other people’s scalps. If you have a weak stomach, you might not want to watch this—but we’re not going to lie, it’s pretty fascinating (and kind of gross at the same time).

In the super close-up of scalps, we see a lot of dead skin and product buildup, which really gives light into how much that stuff clings to your hair follicles and scalp. So really, it’s the product and heat styling that can cause damage, not so much shampoo. In fact, shampoo is the answer. Hint, hint.

So what’s the answer to the initial question—how often should you wash your hair? While it does indeed differ for everyone, Reavey tells us exactly how often most of us should lather up. You might be surprised at the answer! Check out the entire segment below.

How often do you wash your hair? Were you surprised by the answer?