hairdye

Hairdye are cosmetic products used to alter the color of human hair. They can change shade, enhance natural color, hide gray, or achieve fashion tones. Products vary in longevity, from temporary applications that wash out in a few shampoos to permanent colors that last until new hair grows or color is re-treated.

Dyes are categorized as temporary, semi-permanent, demi-permanent, or permanent. Temporary dyes coat the cuticle and fade after several washes. Semi- and demi-permanent dyes may penetrate the outer layer and last weeks, with demi-permanent using a small amount of peroxide. Permanent dyes involve oxidation, where a developer opens the cuticle and deposits color into the cortex.

Common ingredients include color precursors such as aromatic amines (for example para-phenylenediamine in many permanent formulations), oxidizing agents like hydrogen peroxide, and alkalizing agents such as ammonia. Additional ingredients include conditioning aids, pH stabilizers, fragrances, and solvents. Direct dyes are non-oxidative and bind the hair surface without peroxide.

Safety: Some dye ingredients can trigger allergic reactions, so a patch test is advised 24–48 hours before use. Follow instructions, perform a strand test, and apply in a ventilated area with skin protection. If irritation occurs, discontinue use and seek medical advice. Avoid eye contact; rinse if affected. Hair color may interact with existing color and previous treatments.

History: Modern oxidative hair dyes emerged in the 20th century, enabling longer-lasting color and gray coverage. Today, consumers choose among at-home kits and professional services, considering shade level, undertone, porosity, and maintenance.