The word “hair” usually refers to two distinct structures:

  1. the part beneath the skin, called the hair follicle, or, when pulled from the skin, the bulb. This organ is located in the dermis and maintains stem cells, which not only re-grow the hair after it falls out, but also are recruited to regrow skin after a wound.
  2. the shaft, which is the hard filamentous part that extends above the skin surface. A cross section of the hair shaft may be divided roughly into three zones.

Hair fibers have a structure consisting of several layers, starting from the outside:

  1. Cuticle – which consists of several layers of flat, thin cells laid out overlapping one another as roof shingles
  2. Cortex –  which contains the keratin bundles in cell structures that remain roughly rod-like
  3. Medulla a disorganized and open area at the fiber’s center

There are four types of hair: straight, wavy, curly, kinky.

Type 1 is straight hair, which reflects the most sheen and also the most resilient hair of all of the hair types. It is hard to damage and immensely difficult to curl this hair texture. Because the sebum easily spreads from the scalp to the ends without curls or kinks to interrupt its path, it is the most oily hair texture of all.

  • Straight (Fine/Thin) -Hair tends to be very soft, thin, shiny, oily, poor at holding curls, difficult to damage.
  • Straight (Medium) – Hair characterized by volume and body.
  • Straight (Coarse) – Hair tends to be bone-straight, coarse, difficult to curl

Type 2 is wavy hair, whose texture and sheen ranges somewhere between straight and curly hair. Wavy hair is also more likely to become frizzy than straight hair. While type A waves can easily alternate between straight and curly styles, type B and C Wavy hair is resistant to styling.

  • Wavy (Fine/Thin) – Hair has definite “S” pattern, can easily be straightened or curled, usually receptive to a variety of styles.
  • Wavy (Medium) – Can tend to be frizzy and a little resistant to styling.
  • Wavy (Coarse) – Fairly coarse, frizzy or very frizzy with thicker waves, often more resistant to styling.

Type 3 is curly hair known to have an S-shape. The curl pattern may resemble a lowercase “s”, uppercase “S”, or sometimes an uppercase “Z” or lowercase “z”. This hair type is usually voluminous, “climate dependent (humidity = frizz), and damage-prone.” Lack of proper care causes less defined curls.

  • Curly (Loose) – Presents a definite “S” pattern, tends to combine thickness, volume, and/or frizziness.
  • Curly (Tight) – Presents a definite “S” pattern, curls ranging from spirals to spiral-shaped corkscrew

Type 4 is kinky hair, which features a tightly coiled curl pattern (or no discernible curl pattern at all) that is often fragile with a very high density. This type of hair shrinks when wet and because it has fewer cuticle layers than other hair types it is more susceptible to damage.

  • Kinky (Soft) – Hair tends to be very wiry and fragile, tightly coiled and can feature curly patterning.
  • Kinky (Wiry) – As 4a but with less defined pattern of curls, looks more like a “Z” with sharp angles