Hair dyes can cover unwanted gray hair and give you the opportunity to experience what it's like to have hair the shade of any color of the rainbow. Unfortunately, some of the ingredients in hair dyes can be potentially damaging to your hair. For this reason, it's important to understand what ingredients are commonly used in hair dyes and what effects these ingredients have on both your scalp and hair.

One of the most common ingredients in hair dye is ammonia. Ammonia is used in hair dye to open up hair cuticles, and it is mixed with the coloring tint of the dye to act as a vehicle for the color to move deep into the hair follicles, where it can interact with melanin. Melanin is the substance that gives your hair its color. By changing the melanin, the dye can change the overall color of the hair. Ammonia commonly causes itching, irritation and burning when applied directly to the hair and scalp.

Hydrogen peroxide acts as the "developer" in hair dye. When the hydrogen peroxide is added to the ammonia and coloring, the resulting mixture causes the hair to swell. This allows the ammonia to better carry the coloring tint into the hair follicles. Hydrogen peroxide is usually limited to 6 percent in a hair-dye kit, and it is typically combined with water or lotion. The hydrogen peroxide is stored separately from the ammonia and color tint mixture and is only combined just before application. The higher the concentration of hydrogen peroxide solution in the dye, the more sulfur is lost in the hair. Loss of sulfur leads to more damaged and harder hair.

Permanent hair dye can be either oxidation-based or progressive. Progressive hair dyes contain lead acetate and bismuth citrate, the only FDA-approved ingredients for tinting. Both work slowly by reacting with the sulfur of hair keratin.

Oxidation-based hair dye works by using the dye intermediate p-phenylenediamine or the preformed 2-nitro-p-phenylenediamine. The intermediate p-phenylenediamine becomes a dye once a chemical reaction has occurred between the developer and the ammonia solution. The preformed 2-nitro-p-phenylenediamine is already in dye form and added in different quantities to achieve different shades of color.