Demi-permanent colours contain no ammonia but a little amount of peroxide. They require a low-volume developer to slightly open the hair cuticle for the colour to be absorbed. They do not lighten the hair but do a better job at darkening the hair as compared to the semi-permanent hair colours. They also colour the grey hair efficiently without leaving a harsh line of demarcation.
Semi-permanent hair dyes have no ammonia and do not need a developer. The colour gets coated on the outside of the hair and doesn’t penetrate the hair shaft. These colours are also known as ‘stain’ or ‘wash’. They change the hair tone and not necessarily the colour.
Even though demi-permanent dyes cause minimal damage, they slightly open up the hair cuticles which can lead to dry and frizzy hair. Semi-permanent colours only coat the hand strands and wash out quickly.
It varies from person to person depending on the porosity and the health of their hair, vividness of the hair colour and the number of times they shampoo their hair. Both, demi-permanent and semi-permanent colours last anywhere between 4-6 weeks but semi-permanent colours start fading from the first hair wash.
Semi-permanent dyes would probably be a better choice because they fade easily and are easier to remove. But it is necessary to get your hair colourist’s opinion because they are well aware of the condition of your hair and lifestyle.
Both semi-permanent and demi-permanent colours cover up greys successfully. Semi-permanent dyes are better for hair that is minimally grey because they tend to fade quickly. Demi-permanent would give better and longer lasting results.