Hair Color Patch Tests

Hair color and brush
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Q: If demi- and semi- hair colors are basically the same, why is it that a patch test is required for a demi hair color and is not required for a semi hair color?
 
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.
 
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 formulated with smaller color molecules to allow the color to penetrate the hair shaft and deposit color into the shaft of the hair.
 
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See also:
 
How to color hair
 
How to perform a patch test
 
The differences between semi-permanent, demi-permanent and permanent hair color