The Basics of Hair


Hair is the soft, strandlike tissue that covers and protects the body from the elements. It consists of over 95% protein (keratin), 15% water, 6% lipids and 1% pigments. It is the primary source of external warmth for many mammals, providing insulation and cooling (when sweat evaporates from soaked hair) when the body is too cold, as well as protection from UV radiation.

The specialized anatomical structure of hair fibers includes the cuticle, cortex and medulla. The cuticle provides a protective sheath around the outer surface of the hair, while the cortex forms the bulk of the fiber and contains cells that produce melanin pigment, which determines the color of your hair.

Various species of animals, such as fishes and birds, have different kinds of hair and use them for a variety of reasons. In some cases, such as the furs of polar bears, hair serves as camouflage and helps keep cubs warm; in other instances, it functions as a sensory organ that extends the sense of touch beyond the skin surface.

In mammals, hair develops on the head, neck, armpits, genital regions and, in males, on the face and sometimes on parts of the trunk and limbs. The short, slender hairs of the head and neck begin to grow before puberty, and are gradually replaced by longer, coarser hair. These hairs serve a variety of purposes, such as heat and insulation, signaling, sexual recognition, mating, and defense.

Human hairs grow at an average rate of 0.5 inches (13 mm) per month. Each follicle follows its own cycle of growth, rest, fallout, and renewed growth; some follicles have synchronous cycles that cause the total amount of hair to fluctuate.

Some follicles also contain other types of cells, such as keratinocytes, which produce keratin, which aids elasticity and contributes to color. Other follicles produce other proteins, such as collagen and elastin, that are essential for strength.

The morphology of hair varies among individuals and between species of animals, but all hairs have three distinct morphological components: the cuticle, cortex and medulla. In addition, specialized cells, called melanocytes, produce melanin pigment that determines the color of hair and its texture.

While the exact origins of hair are unknown, it is believed that the ancestors of mammals had it in their body as early as 300 million years ago. However, fossil evidence of soft tissues is rare and only rarely shows a mammal’s earliest ancestor with body hair.

To keep your hair healthy and shiny, you should wash it with shampoo that is formulated for your particular hair type, says Raven Hurtado of Maxine Salon in Chicago. Look for one that cleanses your hair without stripping it of its natural oils and is enriched with nourishing ingredients like amino acids, keratin and protein. You should also avoid harsh detergents and sulfates that can dry out your hair, as these ingredients can lead to frizz and breakage.