Dr. Herzog, my scalp often burns when my hairdresser applies highlights and lowlights. Are these chemicals being absorbed into my head and scalp, and is it dangerous?
Dr. Jo Herzog
Dear Reader, this is an excellent question that I get asked quite often from both patients and friends. With the myriad hair treatments being done today, it is reasonable to ask whether these solutions are being absorbed into the scalp.
We know now that the skin absorbs much more than we had believed in the past. We sometimes use the skin to apply medication patches, but the vehicles in these patches are made to promote absorption of the product (medication). Unlike medicine designed for absorption, hair chemicals are not specially formulated to be absorbed, but some certainly can be. How much is absorbed depends on many characteristics of these chemicals.
I do believe that chemicals applied to the skin and to the scalp can be absorbed. When we do clinical trials for drugs that are applied to skin, we measure how much is absorbed, as this is sometimes required by the FDA. However, hair products are not drugs, so even though they are tested, they are neither carefully examined nor regulated. They are simply not held under the same scrutiny.
Some products that we apply to skin are well absorbed. For instance, studies have shown that hydroquinone is one of the best absorbed topical products. Retinoids are also absorbed. Both of these are widely used and very effective products.
As for hair chemicals, hydrogen peroxide that is used for bleaching is hard to absorb unless left on for long periods. Even then, it is metabolized quickly and is probably relatively safe as far as your general health is concerned (although too much too often is not the best thing for your hair).
Inflamed or broken skin will absorb more chemicals than intact skin, so if you have nicks, scratches, or other issues, be careful what you touch. Skin and hair care products do not scare me, although I would be careful of some if I were pregnant. The chemicals that scare me most are pesticides, fertilizers and many of the household chemicals that we touch, spray, and breathe but would not dare to drink. These too, should be used wisely and with caution.