Introduction Hair dyes are among the most widely used cosmetic products worldwide. People use them for aesthetic purposes, to cover gray hair, or to follow fashion trends. Despite their cosmetic benefits, hair dyes contain various chemical substances that may affect hair structure, scalp health, and in some cases general health. This article aims to review the composition, types, and potential health effects of hair dyes. Chemical Composition of Hair Dyes Hair dyes consist of a complex mixture of chemical compounds, including: Ammonia: Used to open the hair cuticle, allowing dye molecules to penetrate the hair shaft. Hydrogen Peroxide: Acts as an oxidizing agent that lightens the natural hair color and helps fix the new color. Coloring Agents: Such as para-phenylenediamine (PPD), which are responsible for producing the final hair color. Conditioning and Stabilizing Agents: Added to improve color durability and reduce hair dryness. Types of Hair Dyes Hair dyes can be classified into several main categories: Temporary Dyes: These dyes coat the surface of the hair and are removed after a few washes without penetrating the hair cuticle. Semi-permanent Dyes: They partially penetrate the hair cuticle and last longer than temporary dyes. Permanent Dyes: These dyes cause chemical changes within the hair structure and provide long-lasting color. Natural Dyes: Such as henna and indigo, which are considered less harmful compared to synthetic chemical dyes. Health Effects of Hair Dyes Improper or frequent use of hair dyes may lead to several health effects, including: Scalp Irritation: Such as itching, redness, and contact dermatitis. Hair Damage: Loss of moisture and protein can result in dryness, breakage, and split ends. Allergic Reactions: Particularly to PPD, which may cause severe reactions in sensitive individuals. Potential Systemic Effects: Some studies have suggested a possible association between long-term use of chemical hair dyes and certain health disorders, although findings remain inconclusive. Prevention and Risk Reduction To minimize the adverse effects of hair dyes, the following precautions are recommended: Performing a patch test before use. Reducing the frequency of hair dye application. Choosing ammonia-free or natural-based dyes when possible. Using appropriate post-dye hair care products to restore moisture and strength. Conclusion Hair dyes are effective cosmetic tools for enhancing appearance and personal expression. However, awareness of their chemical composition and potential health effects is essential. Proper selection and responsible use of hair dyes can significantly reduce health risks and help maintain healthy hair and scalp. Al _ Mustaqbal University, the first university in Iraq