In a classic scene from the movie 鈥淗ow to Marry a Millionaire,鈥� Marilyn Monroe shows off her shapely legs as she sunbathes wearing see-through acrylic shoes and little else. The history of this plastic dates back to 1877 when German chemists Fittig and Paul managed to link together molecules of methyl methacrylate, a colourless liquid, to form polymethyl methacrylate, a tough solid. But it wasn鈥檛 until 1936 that commercial production began under the name 鈥淧lexiglas.鈥�
During the Second World War this novel plastic, being clear and stronger than glass, found applications ranging from submarine periscopes to fighter plane canopies and gun turret enclosures on bombers. And that had an interesting spin-off. Airmen who got shards of Plexiglas in their eyes from shattered airplane canopies fared better than those who were injured by glass splinters. Acrylics turned out to be more compatible with human tissue than glass and did not cause as much inflammation. This observation led to the use of acrylics in the first hard contact lenses.
Acrylics also turned out to be ideal for dentures and found a use in composite dental fillings. Hockey was also a beneficiary, the protective Plexiglas around the rink was far better than netting. But because the plastic doesn鈥檛 have much 鈥済ive,鈥� it has mostly been replaced by tempered glass. Acrylic paints also appeared, basically consisting of pigments and polymethyl methacrylate suspended in water, so there was no worry about solvent vapours.
Then along came acrylic fingernails. One version is made of polymethyl methacrylate and is bonded to the fingernail with yet another type of acrylic polymer, cyanoacrylate glue. There is also the gel type that is painted on to the fingernail and is hardened by exposure to ultraviolet light. That involves some interesting chemistry with the polymerization actually taking place on the finger.
The whole process begins with the acrylic-covered nail being exposed to ultraviolet light that is energetic enough to break chemical bonds, which is exactly what it does to a 鈥減hotoinitiator,鈥� a chemical that is incorporated into the mix. Under the effect of UV, the photoinitiator breaks apart into free radicals that then start the cascade of reactions that result in small molecules of methyl methacrylate joining together to form a giant molecule or polymer. You now have a hardened acrylic nail. Of course, ultraviolet light is energetic enough to break other chemical bonds as well, including those in DNA. That鈥檚 why excessive exposure to the sun causes skin cancer. And that brings up an interesting question. Is there a risk of cancer by exposing the skin on the hands to ultraviolet light while waiting for the acrylic gel to harden?
Some concern about this possibility was generated by two Texas dermatologists in a paper submitted to the Archives of Dermatology in 2009. They reported diagnosing skin cancer on the fingers of two women, aged 55 and 48, both of whom had had previous exposure to ultraviolet nail lights. The first one had a 15-year history of twice-monthly UV nail light exposure, the second had about eight treatments in one year, but that was several years before the first cancer appeared. Such case reports are interesting but they are not very meaningful statistically. Ultraviolet light-cured acrylic nails have been popular for some twenty years with millions of women using them. Any significant risk of skin cancer on the hands would have already been noted epidemiologically. Actually, UV exposure from nail lights is quite small in comparison to exposure from sunlight. Of course, living in Texas exposes one to significant UV.
Calculations show that exposure from a nail lamp is equivalent to spending an extra 1.5 to 3 minutes a day in sunlight between salon visits, the time depending on whether the lamp has one or two bulbs. Basically, the two reports do not make for a compelling case and should not cause panic. The time spent under the lamps just isn鈥檛 long enough to present a significant risk. It is also interesting to note that since the paper originally appeared there have been no further reports of skin cancers linked to nail lights. One would have expected other dermatologists who read the paper to chime in with case histories, as often happens after such publications. It seems there鈥檚 no need to fret about the UV exposure, but anyone still concerned can apply sunscreen to the hands before an acrylic nail treatment. Keep in mind though that in addition to the acrylic monomers and photoinitiators, there are cross-linking agents, reaction accelerators, plasticizers and pigments making irritation and allergic reactions a possibility. Of course, when it comes to acrylic shoes, they can be worn safely. And they鈥檙e still kicking around, in more shapes and styles than ever.
