What is the primary purpose of a smoothing treatment in hairstyling?

The primary purpose of a smoothing treatment in hairstyling is to reduce frizz and make hair more manageable. These treatments typically utilize various chemical processes or products to smooth the hair's cuticle, resulting in a sleeker appearance. By taming frizz, the hair becomes easier to style and maintain, providing a polished look that many individuals desire, especially in humid conditions or for those with naturally curly or wavy hair textures.

The other options, while relevant to hair care, do not accurately represent the primary goal of smoothing treatments. Adding volume generally focuses on creating body and lift in the hair rather than smoothing. Changing hair color pertains to dyeing processes that alter the pigmentation, and removing split ends involves trimming and does not relate to the smoothing effect sought from these treatments. Thus, the essence of a smoothing treatment is primarily centered around managing frizz and enhancing hair's smoothness and overall appearance.