What is ammonium hydroxide primarily used for in hair care?

Ammonium hydroxide is primarily used in hair care for manufacturing permanent hair color because it acts as an alkaline agent that helps to open the hair cuticle. This process is essential for allowing the hair dye to penetrate the hair shaft effectively. By raising the pH, ammonium hydroxide creates an optimal environment for the dye to interact with the hair's natural pigments and the added color molecules. This results in a more permanent and vibrant hair color since the dye bonds to the keratin in the hair.

While other options like enhancing shine, moisturizing treatments, and reducing frizz are important aspects of hair care, they do not specifically relate to the function of ammonium hydroxide. Enhancing shine is typically achieved through conditioning agents or oils, moisturizing treatments involve hydrating ingredients, and reducing frizz often relies on smoothing products or silicones, none of which utilize ammonium hydroxide's key properties.