So, using a dye that includes melanin can produce the same results and without the health risks, say researchers at Northwestern University.
Melanin is a natural pigment that gives our hair colour, but it starts to disappear from hair fibres as we age. To restore colour, permanent hair dyes use ammonia and hydrogen peroxide to penetrate the cuticles in our hair. But the process isn't kind to our hair, it can trigger allergic reactions and could even cause cancer.
Even popular products that use synthetic melanin often contain high levels of heavy metals such as copper and iron, which can also be toxic.
The Northwestern researchers wanted to discover a gentler and safer way to colour hair with synthetic melanin, and found it by using a mild heat and substituting the heavy metals with ammonium hydroxide. Darker hues were achieved by increasing the amount of ammonium hydroxide, and a small amount of hydrogen peroxide gave hair red or gold shades.
The results were the same, and as long-lasting, as from professional dyes and salons, and lasted for 18 washes, the researchers said.