The Basics
of Hair

To understand how color works, you have to start with the structure of hair. Each strand is made up of three distinct layers: the outer layer, or cuticle of the hair, the body of the hair shaft, called the cortex, and the innermost layer, called the medulla. These layers are made from the protein keratin, which is made up of 18 amino acids. The cuticle layer protects the hair and determines how shiny or dull it will look, while the cortex is the main body of the hair, holding in moisture to help it feel strong and resilient.

Porosity

Porosity refers to hair’s ability to absorb liquid, and plays a significant role in the effect of permanent color. Increased porosity in hair is often the result of damage from heat styling, sun exposure, bleach, and other drying factors. It’s important to know one’s porosity level to not only care for one’s hair, but also prepare it for color.

To determine this, simply take a strand of hair and slide fingers from the end upward. If it feels rough, especially toward the ends, your hair is porous. You can help repair overly porous hair by using nourishing oils and deep conditioning treatments containing keratin to help repair any damage, as well as limiting exposure to harsh environments.

How Porosity Affects Hair Color

A porous strand of hair has a lifted or frayed cuticle, which means the hair shaft is not protected, making it easier for permanent hair color to penetrate the hair shaft and deposit a lot of color. This can further weaken already fragile strands and can affect the color result.

Hair that is not porous is called resistant, and often repels and requires more time to process. When coloring hair, it’s important to factor in the hair’s porosity. For highly porous hair, particularly the ends, choosing a shorter processing time will help provide rich, balanced color. For resistant hair, a longer processing time will ensure that color is properly absorbed, and that any grays are adequately covered.