1. Temporary colouring is often used for grey hair. For example, silver shine shampoo takes away the blue or purple tinge from grey hair. However, the hair must be washed regularly with the shampoo to maintain the colour shade. The colour wraps around the hair and comes off when the hair is washed.
3. Demi-permanent colouring does not contain ammonia, which means that no lightening of the hair is possible. Darker shades are possible. However, the toxic nitrogen compound hydrogen peroxide opens the cuticle of the hair, allowing the colour molecules to penetrate the hair.
4. Permanent hair colouring and bleaching. When permanently colouring the hair, first the ammonia and hydrogen peroxide open the hair cuticle. The ammonia destroys the pigments and new pigments are added by tinting.
The aggressive substances contained in the products attack the cuticle of the hair and the scalp, which in the case of a bad reaction can mean that the hairs fall out. But these ingredients are essential for the colour molecules to penetrate deep into the hair shafts. In this way, even extreme colour changes are possible.