What is the fundamental difference between semi-permanent and permanent hair color?

The fundamental difference between semi-permanent and permanent hair color is that semi-permanent color does not contain ammonia, allowing it to infuse color into the hair without altering its natural structure significantly. This type of color typically only deposits pigment onto the hair cuticle and does not penetrate deeply into the hair shaft. As a result, it gradually fades over time, often lasting anywhere from 4 to 12 washes, depending on the specific product and hair care practices.

On the other hand, permanent hair color contains ammonia and a developer, allowing it to penetrate the hair shaft to create a long-lasting change in color. This process opens up the hair cuticle, and as a result, the color is more durable, often remaining vibrant until new growth occurs. The fading that occurs with semi-permanent color is a natural process tied to regular washing and hair care, rather than a feature of the formulation like it is with permanent color.

Understanding the way these two types of hair color work can significantly impact coloring choices, desired outcomes, and maintenance routines for clients in a hairdressing or barbering context.