Which type of hair dye typically causes the most damage?

Permanent dye is typically the type that causes the most damage to hair. This is because permanent coloring processes involve the use of strong chemicals, such as ammonia and peroxide, which work to lift the hair's cuticle and penetrate the hair shaft. This alteration allows for a long-lasting color change, but these chemicals can also lead to significant alterations in the hair structure. The lifting of the cuticle can result in increased porosity, leading to weakened hair that may become dry, brittle, and more susceptible to breakage.

In contrast, temporary and semi-permanent dyes tend to have less intense formulations that don't lift the hair's natural color. Temporary dyes coat the hair without penetrating it, meaning they don't inflict structural changes, while semi-permanent dyes may last longer but still do not provide the same level of penetration as permanent dyes, resulting in lesser damage. Human hair dye can be a bit misleading in terms of phrasing, as it typically refers to dye formulations that are designed to mimic human hair colors and can vary widely in terms of formulation and potential damage; thus, it doesn't directly compare to the others in terms of damage caused by the dyeing process itself.