Haircolor Patch TestsQ: If demi- and semi- haircolors are basically the same, why is it that a patch test is required for a demi-haircolor and is NOT required for a semi-haircolor.
A: I'm not sure where you got your information, but both semi-permanent hair color and demi-permanent hair color should not be used without performing a patch test first to determine possible sensitivity to the ingredient contained therein.
According to MiLady's Standard Cosmetology textbook, both semi- and demi-permanent hair color treatments require a patch test before using on any client. The fact is that demi-permanent hair color does use a very mild formula developer (usually 3 to 7 volume peroxide) while semi-permanent color is merely formulate with smaller color molecules to allow the color to penetrate the hair shaft and deposit color into the shaft of the hair.
How to color hair
How to perform a patch test
The differences between semi-permanent, demi-permanent and permanent hair color