Zoe Diana Draelos, M.D. answers cosmetic questions about hair shine and sunscreen safety
Q.What causes hair to lose its shine after permanent hair dyeing?
18-MEA is covalently bonded to the hair shaft as a monolayer of branched fatty acid with highly hydrophobic properties. This layer resists the entry of water into the hair shaft and adds shine. The ammonia and hydrogen peroxide present in all permanent hair dyes removes this 18-MEA layer from the hair shaft.
Similarly, when the permanent hair dye removes the 18-MEA layer, the hair appears dull.
There is no haircare product currently available that can restore the 18-MEA layer, because once it is removed, the attachment site is quickly oxidized, preventing reformation of the covalent bond.
While hair conditioners applied following shampooing attempt to restore this protective layer, they are easily removed with water contact or the next shampoo application. Of course, they are not bound to the hair shaft and do not create the same kind of shine as the 18-MEA.
Q. Are nanoparticle sunscreens safe?
A. Nanoparticle sunscreens are highly controversial at this time. Basically, it is now possible to create zinc oxide with a particle size of less than 100 nm, which is the defined size of a nanoparticle.
Nanoparticles are not new. Ninth-century Mesopotamian pottery was found to contain nanoparticle-sized glitter.
Nanoparticles are also present in modern big city air pollution, and have the ability to enter the lungs and lodge in the alveoli, inciting an inflammatory response and resultant alveolar damage.
Safety concerns regarding the topical use of nanoparticles resulted in the formation of the Food and Drug Administration's Nanotechnology Task Force, which issued a report on July 25, 2007.
The report echoed the concerns of many scientists in the skincare industry that a better understanding of the interaction between nanoparticles and the skin is required before the particles are widely used.
The concern is that nanoparticles can penetrate the skin, reaching the deep dermis and eventually entering the vasculature for systemic spread.
Zoe Diana Draelos, M.D., is a Dermatology Times editorial adviser and investigator, Dermatology Consulting Services, High Point, N.C.
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