Which ingredient is commonly used in hair color products for its ability to penetrate the hair shaft?

The inclusion of ammonia in hair color products is significant due to its role in raising the hair cuticle, which allows the hair color to penetrate the hair shaft more effectively. Ammonia creates an alkaline environment that not only facilitates the opening of the cuticle, but also interacts with the color formulation, enabling the dye to better bond with the hair. This penetration is crucial for achieving a long-lasting and vibrant hair color.

While hydrogen peroxide acts as an oxidizing agent to develop the color, the primary function of ammonia is specifically related to the penetration aspect. Developer, often a mixture containing hydrogen peroxide, is vital for activating the color but does not penetrate the hair shaft itself in the way ammonia does. Color additives enhance the tint but do not impact the penetration of the dye into the hair shaft. Thus, ammonia's unique capability to facilitate this essential process makes it a key ingredient in permanent hair color products.