Both demi-permanent and semi-permanent hair color dye can be applied at a salon or at home. The are two main differences between demi and semi-permanent hair color: the duration the color lasts and how deeply the dye penetrates the hair shaft.
Chemical Composition
Semi-permanent hair color does not contain any peroxide while demi-permanent hair color may contain low levels of ammonia or peroxide.
Duration
Demi-permanent hair color lasts up to 20 shampoos while semi-permanent hair color only lasts up to 12 shampoos.
Penetration
Semi-permanent hair color deposits dye only on the outermost layer of hair. Demi-permanent hair color deposits dye between the cuticle and cortex of the hair shaft, making it last longer.
Gray Coverage
Semi-permanent is a good solution for hair that has 20 percent or less gray in it. People with a higher percentage of gray hair will see better results with a demi-permanent hair color.
Results
Both semi-permanent hair dye and demi-permanent hair dye enhance natural color tones. Unlike semi-permanent hair dye, demi-permanent hair dye has the ability to lighten hair color.