Most hair tints, dyes, rinses and highlights are chemical-based. The hair analysis deals with mineral content, so hair dyes usually don’t affect it. Bleaching the hair can affect it a little, so it’s best to wait until you have washed your hair 6-8 times after bleaching the hair before taking the sample. It is also best to have washed the hair a few times after dying it before sampling. But overall, it doesn’t make much of a difference. However, medicated shampoos of concern are Selsun Blue (selenium) and Head and Shoulders (zinc). Ideally, for repeat hair mineral analyses, it is nice if you can cut the sample just prior to bleaching or dying. Grecian formula does contain lead which will appear on the hair analysis. Grecian formula is best avoided in general due to this toxicity.