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I subscribe to numerous science and health-oriented newsletters that flood my email inbox every day along with a bevy of unsolicited press releases and blog posts. Broadly speaking, the information provided either warns about some risk in our lives or suggests ways to improve our prospects for longevity. Let me address a typical scare that recently popped up.
I don鈥檛 use nail polish, but I have followed its historical development given the interesting chemistry involved. So, when I was informed by a barrage of posts that the European Union had banned trimethylbenzoyl diphenylphosphine oxide (TPO), a chemical used in gel nail polish, I was keen to look into the story behind the story.
First, let鈥檚 clarify that regular nail polish and gel nail polish employ totally different chemistries and the warning about TPO applies only to the gel variety. Regular nail polish was adapted from paint used by the automobile industry that in turn owes its origin to an accidental discovery. In 1846, Swiss chemist Christian Friedrich Sch枚nbein, as the story goes, spilled a mixture of nitric and sulphuric acids that he wiped up with his wife鈥檚 apron. When he tried to dry the apron in front of the fireplace, he was astonished to see it burst into flames and vanish without leaving a residue. The acids had converted cellulose, the main component of cotton, into flammable nitrocellulose. This came to be known as 鈥済uncotton鈥� and eventually became the source of smokeless gunpowder that is still the major propellant used in firearms today.
Just months after Sch枚nbein鈥檚 discovery, Louis-Nicolas M茅nard and Flor猫s Domonte found that nitrocellulose can be made to dissolve in a mixture of ether and ethanol, leaving behind a plastic film upon the evaporation of the solvents. This is the phenomenon that was exploited by early automobile paint producers. A solution of nitrocellulose and pigments was sprayed on the metal surface leaving a tough, glossy film. A number of fires in the spraying facilities were due to the flammability of nitrocellulose.
In 1917, inspired by the development of automobile paint, inventor Northam Warren introduced the first liquid nail polish. This became a global phenomenon when the Revlon Corporation, founded by the brothers Charles and Joseph Revson, added pigments to the formulation enabling the production of various shades.
Today鈥檚 nail polishes employ the same chemistry although there have been improvements such as in flexibility with the addition of plasticizers. Dibutyl phthalate, historically the primary plasticizer in nail polish, has been phased out in favour of acetyl tributyl citrate or adipate because studies linked it to reproductive and developmental toxicity in animals. Since both nitrocellulose and the solvents are flammable, nail polish has to be kept away from flames.
Gel polishes made their debut in 2009 with chemistry that traces back to the mid-19th century and the discovery that acrolein, a compound produced when fat burns, can be converted into acrylic acid on exposure to oxygen. In the early 1900s, German chemist Otto Rohm discovered that acrylic acid and its derivatives such as methyl methacrylate can be polymerized into transparent, glass-like plastics. This involved the linking of the small molecules, or monomers, into a long polymeric chain, a reaction initiated by free radicals. These highly reactive molecular fragments were in turn were generated by heating benzoyl peroxide to a high temperature.
The novel plastic, named Plexiglas in Germany and Lucite in the U.S., found a quick use in aircraft canopies, acrylic paints and dental resins. By the 1930s, methods to form the needed free radicals for polymerization using ultraviolet light instead of heat were developed. That spurred nail technicians to experiment with applying acrylic monomers and ultraviolet light initiators to nails followed by exposure to UV light to form a tough, shiny layer. The first gel nail systems were marketed in the 1980s and were followed in the 2000s by nail 鈥渟hellacs,鈥� a hybrid system combining gel polymers topped with traditional nail polish. Women took to gels because of the quick cure under a UV lamp and their resistance to chipping. But may gels chip away at our health as well?
One concern is exposure of the skin on the hands to UV light, a known risk factor for skin cancer. Studies have shown that drying lamps can damage mouse and human cells in vitro, but the time needed to do damage is longer than the time a person鈥檚 hands normally spend under a lamp. Still, it is recommended that people who regularly get gel treatment protect their hands with sunscreen. Another concern is about developing an allergic reaction to some component in the gel over time. Since nails aren鈥檛 very porous, the likelihood of gel components passing through the nail into the skin is small. A good technician will ensure that the chemicals do not contact the skin around the nails.
Now for the issue that has scooted across social media, namely the banning of TPO in Europe. This chemical, when exposed to UV light, generates free radicals that start the polymerization process which is critical to the creation of that hard, durable layer on the nails. There has been a number of safety studies carried out on this chemical, a few of which found reproductive toxicity in animals. However, this toxicity was only seen when the chemical was introduced by gavage, meaning direct passage into the stomach of the animal via a tube. Since humans do not consume nail gel, this would hardly seem to constitute a risk. But the European Union assesses hazard, not risk.
A hazard is deemed to exist if a chemical has been shown to potentially cause a problem, irrespective of dose or method of exposure. By contrast, U.S. and Canadian regulators look to evaluate risk, which means taking into account extent and means of exposure. A common tool to assess risk is the MOE, or 鈥淢argin of Exposure.鈥� This is arrived at by calculating the ratio of a substance鈥檚 known adverse effect level to its estimated exposure level in humans. A high MOE means that there is a large difference between the dose that causes harm and the dose to which people are exposed. For a four per cent concentration of TPO in nail gel, the MOE has been calculated to be about 1850. That implies a huge safety margin. In any case, after curing there is virtually no TPO left on the nail.
In Europe, manufacturers will have to abide by the ban and reformulate their gels, which is not a problem since free radical initiators other than TPO are available. On this side of the ocean the chemical can still be present in gels, but for anyone concerned, which I would not be, there are TPO-free products available. I now wait for the next scare that undoubtedly will appear in the deluge of tomorrow鈥檚 emails.
