Eire asks…I’ve been dying my hair red for a couple years and it lasts now because ive been doing it so long. The thing is red dye always has a hard time lasting. I hear this is because the molecule size is too large , BUT I think that’s only regarding the size of the molecules on natural red hair and not dyed hair. With nano technology and improved dye colors and cosmetic formulas why haven’t we found a way to remedy this problem in red hair dye?
The Beauty Brains respond:
Red has always been a difficult color to form, especially in permanent hair color. There are basically three reasons why this is the case:
Fewer choices due to safety concerns
The intermediates (the tiny colorless molecules which penetrate inside the hair and then react to form larger, colored polymers) always seem to be in trouble for safety reasons. That means there are fewer chemicals available for chemists to use.
More easily broken down
The polymers which create the red shades are more easily broken down by UV radiation and other forms of oxidation. Once they’re oxidized their color shifts and they’re more easily removed from the hair.
Size matters
You’re right that in the case of hair dye the size of the molecule is important. But it’s not that the red molecules are too big, rather the problem is they are too small! These red polymers tend to be of smaller molecular size and are therefore more easily removed by water, especially when surfactants are involved (i.e., shampoo formulations).
The Beauty Brains bottom line
You’re right that red is by far the toughest hair color to get and keep. Unfortunately, due to safety concerns, there’s not very much innovation in this area so don’t look for a solution any time soon.