In 1938, a Swiss chemist, Franz Greiter suffered from a sunburn while hiking. This inspired him to invent an effective way to block out the UV rays. In 1944, a pharmacist and an airman, Benjamin Green started using petroleum jelly as a form of physical barrier between the sun and the skin. This worked differently from current forms of sunscreen as these barriers did not absorb the UV chemically but rather just prevented the UV from reaching the skin. In 1962, Franz Greiter formed a standardized measure of UV protection knows as SPF, which is an indication of the fraction of harmful UV rays reaching the skin. Franz Greiter created sunscreen with UVA and UVB ray filters under the company Piz Buin in 1970 having a SPF value of 2 and in 1978, the FDA (Food and Drug Administration) proposes to create a specific set of guidelines to regulate recommending standards for safety and effectiveness. Finally, in 2007, the FDA finalizes its full set of guidelines for standards of sunscreen.
The protection sunscreens provide vary due to their different values of Sun Protection Factor (SPF). There are 2 ways to understand SPF. Firstly, if the average time for an individuals’ skin to go red from the Sun is 30 minutes, an SPF 15 sunscreen would provide protection to last 15 times that duration. Another way to understand it is that SPF 15 sunscreen blocks 14/15 of the harmful rays and only allows 1/15 of UV radiation to reach the skin. Only an average of 30 minutes is needed under sunlight to create a sunburn.
UV rays from the Sun are made out from UVA (320-400nm) and UVB (290-320nm) wavelengths and a mixture of sunscreens protect skin from either wavelengths, or both.(Skin Cancer Foundation, 2013)UVA rays cause premature ageing of skin and causes wrinkling and age spots while UVB rays can burn skin. Hence, UVA rays are given the term “aging rays” while UVB rays are called “burning rays”. It should be taken note that UVA rays cause unseen damage while UVB rays cause painful but obvious damage, hence they are both dangerous in their own ways. Sunscreens which protect skin from both UVA and UVB rays are called broad-spectrum sunscreens.
How UV rays harm the skin
Our bodies already have natural mechanisms when it comes to preventing the overexposure of UV radiation, our skin cells secrete melanin which is a natural pigment that absorbs UV light and releases it as heat. When the skin cells are exposed to large amounts of UV light, the cells are activated to secrete more melanin to protect the cells. Sunburns occur when a layer of skin cells have been exposed to an excess of UV rays and are damaged. Hence, a large amount of blood is redirected to these areas of skin cells to help heal the cells and prevent excessive damage. After a few days, the body removes this part of skin as the damaged cells indicate that large amounts of radiation have damaged these cells and these cells could possibly become mutated and hence the body gets rid of these cells.
The reason why sunscreen can protect the skin from UV rays are due to 2 main type of ingredients in the sunscreen, mineral and chemical filters (Environmental Working Group, 2016)which carry out different roles but ultimately protect the skin. Mineral filters could be seen as advantageous over chemical filters as they are completely harmless to the human skin whereas chemical filters could incorporate side effects. Mineral filters; they deflect and scatter the UV radiation and the most common compounds that are found are – Zinc oxide – Titanium dioxide – Hydrated Magnesium Silicate (Talc).
Based on research done by University of Nantes in France, they compared the efficacy of various mineral filters in absorbing UV rays. The research included the test of common filters found in commercial sunscreen products. These included, Talc, Zinc oxide, Titanium dioxide and silicone coated zinc oxide. The results concluded various things. The effectiveness of UV absorbance in increasing order is as follows; Talc, Zinc oxide, Silicone coated Zinc oxide, Titanium dioxide. These results are peculiar as Talc has been considered by the general public as a reputable photoprotector but when tested, gives a negligible reading of 1 SPF whatever the percentage used. Also, Zinc coated with silicone is the most effective within commercial zinc oxide products. Chemical filters; entirely absorb the UV radiation and usually contain at least 2 of the following.
Also known as benzophenone-3 is classified as an aromatic ketone and provides a broad-spectrum UV coverage. It absorbs UV rays from 270nm to 350nm with its peaks at 288nm and 350nm. It is, however, classified as an 8 on the Environmental Working Group’s toxicity scale which puts it as one of the most toxic ingredients that are found in cosmetic products. When used on rats, oxybenzone and its metabolites accumulate in large amounts in the liver and kidney which sparks off debate whether it should be used in cosmetic products such as sunscreens. It also is an environmental toxin and has been said to cause the bleaching of coral reefs by altering the coral DNA.
Avobenzone is a non-toxic chemical and is approved to be used worldwide to a maximum of 3% and is able to absorb the full spectrum of UVA rays and a partial range of UVB rays to the greatest absorption of 357nm. However, Avobenzone is not very stable on its own and degrades quickly under light, hence other photostabilisers like octocrylene and octisalate are used instead but are considered toxic.
Otherwise known as Octyl Salicylate, is a water-resistant organic compound with a salicylic acid condensed together with an ester. The salicylic acid part of the molecule is responsible for absorbing UVB rays in UV light. For cosmetic products containing less than 5% of Octisalate, it is not considered toxic and is used to stabilize avobenzone.
It is formed from an ester when reacted with an acrylate and 2-ethylhexanol and absorbs UVA and UVB rays from 290nm to 350nm. It is photostable and does not degrade under sunlight and also helps other substances from being photodegraded as well. The downside is that octocrylene is very easily absorbed into the skin and has been shown to produce reactive oxygen radicals which could affect DNA structure.
Homosalte is formed when an ester, salicylic acid and 3,3,5- trimethylcyclohexanol are reacted together and absorbs UVB rays from 295nm -315nm. (Smart Skincare, 2016) The molecule is hydrophobic and thus does not dissolve in water. It is considered to be a weak toxin as well a weak endocrine disruptor.
Also known as octyl methoxycinnamate, it does not dissolve in water and absorbs UVB rays with and absorbance from 280nm – 320nm. This molecule also breaks down to form harmful radicals and can also enter the endocrine system.
Why do sunscreens have to be re-applied
There exists a process called photodegradation where a molecule is broken down from the absorption of photons and is the combination of the processes, oxidation; the loss of electrons and hydrolysis; the addition of water causing the splitting of chemicals. The reaction initiates with a photon that enters its excited state and passes its energy to an electron. Due to this energy, spontaneous oxidation occurs with ozone and forms oxidation radicals which are highly reactive and these degrade organic compounds that can be found in the atmosphere.
A UV visible spectrophotometer works by comparing the intensity of light after passing through a sample and compare it in a ratio to the original intensity. This ratio is calculated to find the value of a transmittance value. This intensity is calculated from energy that the electrons present on the compound possesses. When a compound is exposed to light energy that resonates with a difference in electron energy level, their electrons are able to jump from their original ground state to a higher level, their excited state. This process is highly precise and the amount of light Fig1: (the excitation of electrons to a higher energy level after resonating with light energy)energy supplied must be similar to the difference in the excited and ground state to allow the electron to be promoted to a higher level. This process is carried out from the outermost electron all the way to the innermost electron. Once the transmittance values are obtained, it is put back into the formula A = 2 – log10 %T where A is absorbance and T is transmittance.
Sunscreen conditions and the lack of sunscreen use on a daily basis
Typically, people apply sunscreen only when they feel that they are prolonged to long hours under direct sunlight. The truth is that even when under the sunlight for short periods of time or when under the shade, an individuals’ skin can still be exposed to UV rays. Most windows used only can filter out UVB rays but allows UVA rays to pass through easily. An important condition that sunscreen has to have is to be waterproof. Based on the FDA’s guidelines, a sunscreen has to remain effective when exposed to constant water after at least 40 minutes. Sunscreens that are unable to provide this protection are not legally allowed to mention that they are waterproof or water resistant. Most people only use a quarter to half the amount of the recommended 1 ounce of sunscreen for their entire body.
Furthermore, at a specific outdoor event surveyed by University of Minnesota in Minneapolis, even when giving out free sunscreen at booths, only 33% of people applied sunscreen to all sun exposed parts of their body, and this data only applied to when it was a sunny day.
Misconceptions of UV rays and sunscreen use
There are fewer UV rays from the sun on cloudy days -This is correct to a small extent, there are less UV rays reaching the skin but 80% of the harmful rays still could reach the skin. This is still a large amount and sunscreen should still be used to prevent any harm.
Water resistant sunscreen only needs to be applied once when exposed to sweat and water – This is false. Although sunscreen is waterproof or water resistant, it still needs to be reapplied every 2 hours when in water.
Sunscreen only needs to be applied when exposed to sunlight – This is false. Sunscreen should be applied 30 minutes before exposing the skin to UV rays. This allows time for the ingredients to properly bind with the skin and provide its full protection.
A sunburn is an indication that insufficient sunscreen has been applied – This is true but even without a sunburn, the skin could have been heavily affected by UV rays. This is because a sunburn is only formed from the overexposure of UVB rays and not UVA rays, which are just as harmful.
SPF 100 provides twice as much UV protection as SPF 50 – The actual UV protection is negligible. SPF 50 sunscreen provides 98% UV protection while SPF 100 provides 99% UV protection, and this is assuming that the consumers apply the right thickness of sunscreen and constantly reapply these layers.
How do UV rays from the sun affect skin cells and how does skin cancer arise?
The specific type of cancer that forms in overexposure of UV is called non-melanoma skin cancer which originates from cells other than melanocytes, cells that produce melanin, and are thus found in basal cells or squamous cells. Basal cells make up the bottom layer of the epidermis which is known to continuously divide and push older cells to the surface of the skin. These cells are the ones responsible for the quick growth of skin. However, due to their nature of continuous division, they are especially susceptible to being altered by the UV rays to produce cancer cells. The squamous layer is the layer right above the basal layer and contains the divided basal cells that have been pushed upwards. They secrete keratin, a protein which can be found on skin, nails, hair and is used for protection as it is a hard protein. Based on the American Cancer Society, every year, more than a million cases of non-melanoma skin cancer diagnosed are due to overexposure to UV rays from the sun and is responsible for 8,110 deaths that year.
Now how UV rays alter DNA will be discussed. UVA rays are less energetic than UVB rays and thus does not alter or damage the DNA strand directly. Instead, it causes the formation of oxygen radicals which could either react with the DNA strand directly or alter fats or proteins making them harmful to DNA. Hence, UVA rays do not cause sunburns or skin cancer but it increases the rate of melanoma and photodermatitis. UVB rays contain much more energy and causes a change in structure after it hits the DNA. UVB rays will only react with the DNA molecule if there are 2 thymine bases in a row, and will alter a bond found in the thymine. This bond causes the fusion of the 2 thymine bases to form what is known as a dimer. These dimers cause a kink in the DNA which might affect the transcription of the DNA which ultimately produces a nonfunctional protein. The reaction of UVB rays and DNA is highly dangerous as up to 100 dimers can be made just by passing over DNA under the presence of UVB rays. However, the cells have their own mechanism to overcome the production of dimers. Specialized proteins in the cell identify the presence of dimers and remove the damaged section of DNA and replaces the thymine bases.