Hair is one of the most recognizable characteristics of mammals. It provides insulation, it protects against sun and wind damage to the skin, and it serves as a means of expression and communication. Hair is a keratinous filament that grows out of an epidermal penetration in the dermis called a hair follicle, which is anchored deep into the skin. Hair is a multi-layered fibrous protein called keratin (pronounced kair-teh-nin), which also makes up nails and the outer layer of your skin.
Most people have one or more hairs growing from their head, and many have some on their arms, legs and torso as well. Hair can be quite a distinctive feature and it often tells something about a person’s culture, religion or region. It can even be a sign of health or wellness.
The human body has two types of hair, vellus and terminal. Vellus hairs are soft, fuzzy hairs that can be found all over the body and serve a primary function of insulation. Terminal hairs, on the other hand, grow from the scalp and are usually coarser than vellus hairs. Hair can be straight, wavy or curly in texture and it comes in a wide variety of colors and textures.
Almost all humans have some hair, although women tend to have fewer vellus hairs than men and their hair is usually darker than that of men. The color and texture of hair is influenced by genetics, hormones and a healthy diet that includes plenty of protein and vitamins. Hair can slow down or stop growing in response to certain hormonal changes, such as a drop in estrogen levels that occurs during the menopause.
Hair follicles are located in the lower dermis layer of the skin. Each follicle is in the shape of a tiny cylinder with a rounded bottom in the skin and is surrounded by a thin layer of fat. The follicle is attached to an oil gland called the sebaceous gland, which produces lipid-rich sebum that naturally helps to keep your hair and skin moisturized.
As blood vessels supply nutrients to the hair follicle, new cells grow inside the follicle and eventually push older cells up through the skin’s surface as a hardened filament we know as hair. This process is known as keratinization. Hair has three distinct layers that are visible when seen on a microscopic level: the cuticle, the cortex and the central medulla. All of these layers work together to give hair its strength, elasticity and color. The medulla is especially important because it gives hair its shiny appearance.