What is the function of a toner in hair coloring?

A toner is used in hair coloring primarily to neutralize unwanted undertones in the hair. After the initial coloring process, especially with bleaching or lightening, hair can have brassy, yellow, or orange undertones that may not be desirable. Toners are specifically formulated to adjust these undertones, often employing color theory to deposit pigments that counteract the unwanted shades. For instance, a purple toner can be used to neutralize yellow tones in blonde hair, as purple is opposite to yellow on the color wheel.

While adding shine, making hair softer, and preventing breakage are all benefits that may relate to hair care and coloring, these functions are not the primary role of a toner. Shine can be enhanced by various glossing products, softness relates more to conditioning treatments, and preventing breakage is typically addressed with specific strengthening products or treatments rather than through the use of a toner.