Although there seems to be only one letter to separate a semi-permanent and demi-permanent hair dye. There are a few differences that separate them from each other.
Semi-permanent dyes are temporary dyes that do not require mixing.
- Does not contain bleach (cannot lighten hair); brings out more natural color and blends gray hair with natural hair color.
- Can last up to 3-6 weeks (depending on the dye and number of times hair is shampooed a week.)
- The color progressively fades with shampooing and exposure to air.
- May need to be frequently applied but this may be damaging to hair.
Demi-permanent dyes are also temporary dyes but they require mixing with a developer which will open the hair cuticle so the pigment can get onto the hair cuticle but not penetrate it.
- Does not contain bleach (cannot lighten hair); can darken hair color, blend gray hair with natural hair color, tone highlights and refresh hair color.
- Can last longer than semi-permanent dyes; Up to 4-7 weeks (depending on the dye and number of times hair is shampooed a week.)
- Permanent dye can be applied on top of demi-permanent dyes or vice versa. However, gray hair may not be fully covered by the demi-permanent formula.
As always, you should be wary of using dyes and their effect on your hair. Consult with your hair stylist or read reviews and do some research on the formula. Some organizations still accept hair that is dyed, as long as its grown out or has not been too chemically treated. Email your organization to ensure that your hair can still be accepted if you are interested in semi/demi-permanent dyes and still want to donate your hair!