Way back in the olden times (or 1908), hair care regimens were pretty lax. Women were advised to wash their hair no more than twice a month, with most people shampooing only once a month.

Then, marketing campaigns began to push us to wash more and more frequently, to such an extent that Americans lather up an average of 4.6 times a week. That’s about 18 times more frequently than in the past!

So really, how often should we be washing our hair with shampoos and conditioners?

An increasingly popular answer is “never.” The unfortunately-named “No Poo” method is in favor of the “all natural” approach. The most popular way of doing that is by replacing shampoo with dissolved baking soda, which does a decent job of washing hair. That is followed by diluted apple cider vinegar, which acts as a conditioner. The idea is that the baking soda will strip your hair of oils—both its natural oils and the oils that you are trying to wash away. Then, the apple cider vinegar will act as a replacement for your natural oils, which your hair needs.

The “No Poo” method sounds great, but some dermatologists have concerns. Baking soda is a known alkaline irritant with a pH of 9, which makes it really tough on your hair. According to Dr. Hudrey Kunin, M.D., alkaline shampoos can cause dehydration, leading to extremely fragile hair. Though baking soda can soften your hair at first, it can ultimately lead to brittle locks that are prone to breaking.

The apple cider vinegar is less controversial. It can fight some fungal infections, which is comforting. But like all things, too much can have a negative effect. In this case, it has a tendency to make hair become lighter, drier, and more brittle as well.

That isn’t to say that the “No Poo” approach won’t work. It depends largely on the individual head of hair, so if you want to try it out then go ahead.

If you don’t want to stop shampooing, then you’re in luck. ScienceAlert and the Columbia University health column agree that people with dry to normal hair only need to wash their hair “once or twice a week.” Greasier hair will need to be washed more often. Coarse/curly hair can sometimes be washed once a week, but people with straight hair will need to shampoo more often. Hair damaged by styling should be washed less often than healthy hair.

Of course, washing your hair daily can be okay too. As long as you use a gentle shampoo, your scalp should not be stripped of essential oils, and your hair will be fine.

But no matter the hair type, there are a few rules that everybody should follow.

When shampooing, you should focus on your roots, and avoid the ends of your hair (if you can—sorry to people with short hair). When using conditioner, focus on the mid-shaft to the ends of your hair, not your scalp.

Speaking of conditioner—it’s essential. It provides moisture and protection that shampoo can’t, so just use it.

When you finally rinse out your hair, use cold water. It’s not exactly pleasant, but “[it] will help to close the cuticle and seal in moisture from the conditioner,” says Good Housekeeping.