Permanent hair dye is formulated to penetrate the hair strand’s natural outer barrier and deposit color molecules deep inside the hair shaft.
But the process of getting the color molecules there can be damaging.
The outer barrier of the hair is called the cuticle. Its transparent protein cells are tightly bound together and coated with a lipid layer that can help repel water, giving hair its natural shine and integrity.
Hair dye breaks down the lipid layer and swells the hair strand. This swelling lifts the cuticle and allows small color molecules to pass through to the center of the strand. A chemical reaction then occurs inside the hair strand, creating larger color molecules that are trapped within the hair, resulting in a new hair color.
Removal of the lipid layer and a damaged cuticle can reduce your hair’s natural shine, make it feel rough and result in increased porosity. So other molecules, such as water, can move in and out of the hair strand more easily and make hair susceptible to further damage.
So when it comes to keeping colored hair healthy and making hair color last longer, protecting the hair structure and keeping the new color locked inside is key.