It may come as a surprise that shampoo is formulated to clean and remove oil from your scalp and roots rather than your entire head. In fact, working shampoo all the way through to the ends of your hair can eventually dry it out, Healthline says. It's better to focus about 2 teaspoons of shampoo on your scalp (via Head & Shoulders) and let the ends get clean as the lather trails down to the ends. How many times a week you should repeat this exercise can vary, but only people with extremely oily hair may need to use shampoo every day (via Good Housekeeping). For everybody else, two or three times a week should suffice.

Oiliness is a big determining factor in how often you should wash your hair, but it's not the only one. Your hair type plays a role, too, with thick, wavy, or curly hair generally needing less washing. Thin or straight hair usually contains more sebum (a natural oil). How many, how much, and which type of styling products you use matter too. They can build up and leave hair feeling heavy and limp.

Keeping your activity and perspiration levels in mind, Healthline advises shampooing hair when you notice excessive oil production and your hair feels greasy. For some people, this translates to "co-washing," which means "conditioner-only washing" and forgoing shampoo entirely (via Real Simple). Understandably, then, people who decide to shampoo less often may be more amenable to taking a closer look at the shampoo they use, as well as its price.