Hair is a thin structure that grows from the skin of every mammal. Like horns and nails, it’s made of a protein called keratin. Each individual strand has a root and shaft. The root lies under the skin in a pit known as a hair follicle, which is filled with living cells that constantly multiply and push older cells out through the surface of the skin. Once the cell reaches the surface, it’s considered dead and can be cut without causing any pain. The slick, silky-smooth outer layer is called the cuticle. Its flattened, overlapping cells give the hair its luster and protect it from water, sun, and chemicals.
Hair’s primary function is to regulate body heat, but it can also provide camouflage, protection, and communication. For example, polar bears’ transparent fur helps them blend in with snowy environments, while their tusks and whiskers serve as defense by warning potential predators of their size. In humans, the hair on the head acts as insulation and keeps the skull from absorbing too much sunlight. Eyebrow hair keeps sweat and other particles out of the eyes, and the lashes keep dirt and dust away from the sensitive areas around the nose and mouth.
In addition to its thermal regulation functions, hair can be used as a means of communication between animals. In some cases, such as for female dogs, it’s a way of signaling the availability of mates. In other animals, such as squid and sharks, it’s a means of communicating with other squid or sharks. And in some mammals, such as polar bears and giraffes, the hair is used to make signals of territorial or threatening behavior.
Humans use hair to make clothes, hats, and other textiles. They also use the hair of rabbits, foxes, and mink to make fur coats. The hair of sheep, goats, and camels are also used to make wool, which is a soft, warm fabric.
Many people use shampoos to help their hair look and feel healthy. These products clean the scalp and strands, and they can also remove product buildup that can cause dullness or frizz. However, not all shampoos are created equal, and some may strip the hair of its natural oils, leading to dryness or other problems.
GH Beauty Lab’s editors tested several hundred shampoos to find the best formulas for different types and concerns. The best shampoos will thoroughly cleanse the strands, without leaving them feeling dry or stripped of their natural oils. They will leave the strands shiny, smooth, and easy to style. And a good shampoo can even help prevent split ends by protecting the cortex from harsh treatment, such as hard brushing or overexposure to sun and water. The top shampoos in our test consistently left hair looking and feeling great, from drugstore value picks to luxury picks for all budgets.