Q: I need monthly hair color touch ups to cover my grey roots. When I go for these touch ups, my hairdresser always colors my entire head. Is this necessary? Won’t I end up with all different hair color shades
after a year’s growth since the thickness of the hair color layer will be different depending on the number of touch ups a certain part of the hair has been going through?
A: Well, if haircolor worked like paint, this would certainly be a concern. If that were the case, the hair at the ends would also become thicker and heavier the more it grew, unless you cut it regularly as well.
But the fact is that haircolor deposits color into the shaft of the hair through the chemical process that develops the color. Because the color developing process is limited in
time, there’s only so dark that the color can become. This means that the pigments being developed are more controllable.
It is typically the practice to apply the color to the new growth on the hair, and allow it to process for a small amount of time, then apply the color to rest of the hair in order
to freshen the color up again. (Sometimes haircolor can fade in between retouch services.) This is probably what your stylist is doing when she applies the color in your retouch service.
However, you need not to worry about the haircolor “building up” on the hair. The only problem that could potentially arise, if improperly applied would be that the hair along the ends was
darker than at the scalp. However, if this was going to be an issue, the problem will be apparent immediately after the color is applied.