Nail Polish
INTRODUCTION TO NAIL POLISH
Nail polish, also known as nail varnish, is a type of thick, viscous lacquer that can be applied to the surface of the nail plate fingernails and toenails to decorate, beautify and protect. It is one of the most widely used cosmetics as it is non-invasive and is easy to use and apply. Nail polish comes in a variety of colours, style and even textures and is easily accessible, creating a large attraction towards this cosmetic product. The main purpose of nail polish is for cosmetic beautification; however, it can also serve as a purpose to camouflage any nail textures. [1]
TYPES OF NAIL POLISH
There are two types of nail polish: conventional and gel.
Conventional nail polish is most commonly made of a polymer known as nitrocellulose which is dissolved in a solvent (usually butyl acetate or ethyl acetate). [2] Nitrocellulose is the film-forming agent, which ensures the nail polish to adhere to the surface of the nail plate after the solvent evaporates. [1,2] Nitrocellulose is oxygen-permeable, which allows the maintain nail health. [1] Conventional nail polish also contains adhesive polymer resins such as toluene sulphonamide formaldehyde, which helps to improve gloss, strength and flow to the polish. [1,3] After application, the polish is left to dry. [2,4]
Gel nail polish is an alternate formulation which contains photoinitiators which react in wavelengths of 340-380nm and methacrylate monomers. [1,5] In comparison to conventional nail polish, instead of leaving the polish to dry, the polish is applied in layers and each layer is exposed to ultraviolet light, especially UVA. [5] The exposure of UVA helps to initiate a polymerisation process which solidifies the nail polish. [1] After the gel nail polish is applied on the nail surface, it is placed into a UVA lamp to be cured, turning the liquid polish into solid. The photoinitiator readily absorbs the UVA which creates free radicals - species that contains an unpaired electron. These free radicals cause a large number of monomers to join into long polymers through the process of radical addition polymerisation. When a bond absorbs UV radiation at the right wavelength, the bond undergoes homolytic fission which is the breaking of a covalent bond where each of the bonding electrons leaves with one of the bonded atoms, forming a free radical. This process is known as the initiation step. Due to the unpaired electrons in the free radicals, they would quickly pair up with another electron from another bond, usually the double bond in the methacrylate monomer, causing two more electrons being separated. One of the electrons will bond with the free radical and the other electron would remain unpaired - forming a new free radical. This process is known as the propagation step. This newly formed radical may then attack another methacrylate monomer. This cycle repeats, forming a chain reaction until a long polymer chain is formed. The chain reaction would end when the two growing chains of polymers collide, known as the termination step. [6]
Both conventional and gel polish contain plasticisers such as camphor, dibutyl phthalate and dioctyl phthalate which enhances the flexibility and adhesive properties of nail polishes by linking themselves into the polymer chains in nail polish and increasing the distance between the small chains. These compounds prevent the polish from cracking or chipping easily. [1,6]
Both types of nail polishes have to be applied in thin coats. For conventional nail polishes, then coats are required as thick layers of polishes are hard to dry whereas for gel nail polishes, thin coats are necessary as UV light cannot penetrate through thick coats of polish. [6]
NAIL POLISH APPLICATION
Most of the time, three variations of nail polishes would be used, whether it be conventional or gel. A layer of a transparent base coat would be applied on the surface of the nail which strengthens the nail plate by decreasing the water loss. It has high concentrations of resin which allow stronger adhesion of the coloured polish onto the nail. Base coats help to restore moisture in the nail as well as to fill in any ridges on the nail surface. A few layers of the coloured polish would then be applied above the base coat. As the layers of coloured polish increases, the opacity of the nail colour increases. A layer of transparent top coat would then be applied to finish the nail look. Top coats contain more nitrocellulose than resin which helps to prevent the nail polish from chipping. [1]
RISKS OF NAIL POLISH
There are no major risks of nail polish, but there are some ingredients that can be potentially bad for the user. Toluene sulphonamide formaldehyde has the potential to cause cancer as well as allergic contact dermatitis which means that is can make the skin itchy, dry and cracked. [7,8]
BIBLIOGRAPHY
[1] Chandra, Somodyuti, and Anupam Das. “The Science of Nail Polish, Nail Polish Remover, and Nail Moisturizers.” Nail Disorders, 2019, pp. 497–501.
[2] “The Chemistry of Nail Polish – Polymers, Plasticisers and Pigments.” Compound Interest, 6 Apr. 2017, www.compoundchem.com/2017/04/06/nail-polish/.
[3] Helmenstine, Anne Marie. “How Nail Polish Works and What It's Made Of.” ThoughtCo, 4 Nov. 2019, www.thoughtco.com/nail-polish-chemistry-603996.
[4] Valenty, Vivian B., et al. “Polish College: The Basics.” NAILS Magazine, 1 June 2008, www.nailsmag.com/389523/polish-college-the-basics.
[5] Roy, Sree. “The Science of Gels: How Gel Nail Products Work.” NAILS Magazine, 14 Mar. 2011, www.nailsmag.com/387143/the-science-of-gels-how-gel-nail-products-work.
[6] Husband, Tom. “How Varnishing Your Nails Is like Making Plastic.” The Mole, Jan. 2015, issuu.com/rsc_eic/docs/the_mole_january_2015.
[7] Nassim, Janelle, and Kristina Liu. “A Look at the Effects of Nail Polish on Nail Health and Safety.” Harvard Health Blog, Harvard Health Publishing, 30 Oct. 2019, www.health.harvard.edu/blog/a-look-at-the-effects-of-nail-polish-on-nail-health-and-safety-2019112118231.
[8] “Contact Dermatitis.” NHS, www.nhs.uk/conditions/contact-dermatitis/.
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