Over time, there have been dozens of myths regarding the way hair grows. "The Encyclopedia of Superstitions, Folklore and Occult Sciences of the World," first published in 1903, presents a few: If you cut your hair on a Sunday, it won't grow, and if you get a haircut on Friday, you'll learn of a death before it grows back to its original length. If you want your hair to grow quickly, put some trimmings under a growing plant. If you want lots of hair, take a scoop of water from a running brook -- with the left hand, mind you -- and pour it over your head [source: Daniels, Stevans].

These ideas seem silly to us now, but one belief about hair growth still seems iron-clad: If you want your hair to grow, you should get regular trims. It seems counter-intuitive, but stylists swear up and down that it's true. Is it, or is this claim just a way for hair salons to stay in business? Do stylists rob us blind by insisting that we come before them every six to eight weeks?

It's best not to disagree with people who wield sharp scissors near your head, but in this case, the stylists are wrong -- a haircut has no effect on how fast your hair grows. Whether you trim it or not, hair grows about half an inch (1.3 centimeters) every month [source: Foss]. That growth rate won't speed up if you take more hair off the bottom, and if you're trimming off more than that each month, then you cut off all the new growth. The only factors that have been proven to affect the rate at which hair grows are genetics, hormones and diet [sources: O'Connor; Monsma].

It's true that frequent trims can make hair look healthier, particularly if the chops eliminate split ends that may in fact be impeding growth. But if you want long hair, it's better to prevent those split ends in the first place by avoiding heat and overstyling, rather than sacrificing your half-inch of hair growth to the stylist's scissors.