In our previous article, we looked at temporary hair colouring. This is for those who want to experiment with dye without the long term commitment. However you might be feeling brave enough to delve into permanent colour. Before you do so, here’s what you should know.
Unlike temporary dye that coats the hair shaft, chemical hair colouring works on the inside of the strands. The cuticles on the hair shaft are opened then the colour is deposited. This is an irreversible chemical reaction. When bleach is used, it reacts with the melanin in hair, removing the color. The melanin is still present, but the oxidized molecule is colorless. Hydrogen peroxide is the most common bleaching agent.
Permanent hair colours usually involve a simultaneous two-step process. The original colour of the hair is removed first then the new colour is deposited. Ammonia in the dye opens the cuticle and allows the hair colour to penetrate the cortex of the strands, while hydrogen peroxide removes pre-existing colour by breaking the strands’ chemical bonds.
Ammonia present in the hair dye provides an alkaline environment for the reactions to occur. Ammonia causes the cuticles to swell, which then allows the dye molecules to pass into the hair and induce permanent colouring. If you’re a fan of frequent hair bleaching, be warned that this process can damage your strands.
Most people don’t have negative reactions to permanent hair dyes. However just to be safe, have your stylist do an allergy test 48 hours before applying the dye in order to guard against severe allergic reactions.
Fun Fact
French chemist Eugene Schuller developed the first safe commercial hair colour in 1909 by using the chemical paraphenylenediamine (PPD).
Hair’s natural hair colour is determined by two types of melanin: eumelanin, and pheomelanin. The former causes shades ranging from brown to black, whilst pheomelanin gives colours in the range of blonde to red.
