The team describe the findings as a mild alternative to traditional products
A team of researchers has developed a hair dye made from synthetic melanin.
Melanin is a natural pigment that gives human skin, hair and eyes their colour.
Traditionally, high concentrations of toxic metals copper and iron, and strong oxidants, were required to use synthetic melanin to dye hair.
However, scientists at Northwestern University, US, found that they could substitute mild heat and a small amount of ammonium hydroxide for the heavy metals and strong oxidants used in previous formulas.
Despite the use of ammonium hydroxide (ammonia), the researchers claim the new process results in a milder formulation than traditional hair dyes.
Coloured hair is said to last for at least 18 washes. Darker shades were developed by increasing the concentration of ammonium hydroxide, or red and gold shades by adding a small amount of hydrogen peroxide.
"Overall, the conditions were similar to or milder than those used for commercially available hair dyes," reported the team.
"The natural-looking colours deposited on the hair surface, rather than penetrating the cuticle, which is less likely to cause damage."