A preparation such as a lotion applied to the skin to prevent sunburn by chemically absorbing ultraviolet radiation’, is the official definition of Sunscreen according to Merriam Webster. Sunscreen protects our skin from the harmful effects of UV rays not just by absorbing them, but also by either scattering, blocking, or reflecting UV rays. (1)
Sunscreen protects us from the harmful effects of UVA and UVB rays, both of which have their own specific effects but overall, cause sunburn, inflammation, rashes, and skin cancer. (2) Among these effects, sunburn is the most common consequence of UVA and UVB exposure.
Reports from recent studies proving the association between UV exposure and skin cancer have led to a massive surge in the use of sunscreen in the general population, especially Caucasians due to their low melanin content. It is absolutely true and scientifically verified that this increased use of sunscreen is beneficial, but this may not be the case for everyone as most people using these lotions don’t use them correctly. Proper application and reapplication are extremely vital for the proper function of sunscreens, but this key point is often carelessly ignored.
Proper Use of the Ideal Sunscreen
The optimal sunscreen should not just block or scatter the UV rays, but it should also protect the skin from the formation of free radicals which can cause DNA damage, and in the long run, can result in potentially fatal skin cancer. Along with that, it should also stay on the surface of the skin for a certain period of time before coming into contact with water while swimming to prevent it from being easily washed out. (3)
The efficacy of these agents is measured separately for UVA and UVB protection. Protection from UVB is measured through SPF, or Sun Protection Factor, which is basically the ratio between the radiation levels required to damage sunscreen protected skin and radiation levels required to damage normal, unprotected skin. Studies have shown that the minimum effective SPF is 30. (4)
Protection from UVA is not measured through SPF but rather through immediate pigment darkening response in vivo (as applied), however, it only shows accurate results with low levels of UV rays. An in vitro method to measure the protection from UVA is through measuring the UVA Protection Factor and applying it to the IPD response spectrum using the COLIPA guidelines, which have already been accepted and applied in Europe. (5)
Choosing the best product alone is not enough though. The efficacy of the sunscreen also depends on the technique used by individuals. The FDA and many other countries have guidelines that clearly state the way to properly apply these agents.
According to the FDA, sunscreen should be applied adequately, and liberally with the adequate product quantity of 2mg/cm2. In addition to that, it should be reapplied according to the instructions on the box. Also, sunscreen should be reapplied after swimming or sweating, as it can be easily washed away. Even if a water-proof sunscreen is used, it is important to know how long it stays waterproof so that proper re-application can be done. According to studies, individuals often do not comply with these instructions, and therefore face the consequences of exposure to UV rays despite having, whilst incorrectly, applied sunscreen.
Which Sunscreen Is Best for You?
To choose the best sunscreen, it is important to know the basic ingredients of sunscreen. As mentioned above, sunscreens have filters, and they are of two types:
- Organic (salicylates and benzophenones), which absorb UV and convert it into heat.
- Inorganic (titanium dioxide and zinc oxide), which either scatter or reflect UV rays.
Out of the two, inorganic is the least irritating to the skin. Many studies show that the best sunscreen to use is a broad-spectrum agent as they prevent UV-radiation induced gene expression both in vivo and in vitro. (6)
The perfect sunscreen for you also depends on your skin type, which depends heavily on the melanin content of the body. Melanin is the body’s own sunscreen and it acts as a shield against UV rays. It is also responsible for determining our skin colour. (7) Out of the two types of melanin, Eumelanin and pheomelanin, Eumelanin plays an important role in protection from UV rays.
The natural protection from melanin may give rise to the misconception that dark-skinned people with high levels of melanin are naturally protected from UVR. That is not true, and studies have found them to have a natural SPF of around 13, which as discussed above is not enough.
According to Fitzpatrick Skin Type Classification, there are six types of skin, ranging from I to VI, with VI being the darkest and I being the fairest. In a study conducted in Beuth University of Applied Sciences, Berlin, they found that even the type VI skin underwent radical formation after UVR exposure, albeit later than type II to V skin type. Hence, concluding that even type VI skin needs sunscreen, like the rest of the skin types. (8) All skin types need at least SPF 30 sunscreen. Although, studies have shown SPF 100+ works more efficiently than SPF50 for all skin types. (9)
Figure 1 – Fitzpatrick scale modified from Adapted from Fitzpatrick’s Dermatology in General Medicine. McGraw-Hill Professional; 5th edition.
Limitations of Sunscreen
Most of the limitations of sunscreen are due to individual inadequacy in following instructions. As mentioned above, it is crucial to apply a thick layer of the agent, along with re-application every couple of hours or 40 minutes if going swimming. Using a broad-spectrum antibiotic is very important, preferably with insect repellants so as to prevent insect-borne infections. (1)
Also, just like any other topical cream, sunscreen agents are made of chemicals that may be allergens for some people. Hence, it is important to know the specific allergens for you to be able to choose the perfect sunscreen agent for your skin. Sometimes, the allergens may actually be the preservatives, or the fragrances added, and it is safe to avoid such products. It is also important to not use body sunscreen on the face as they may cause acne or rashes. Furthermore, it is important to use non-oily sunscreens if you have acne-prone skin. Normal sunscreens may make acne even worse and only non-comedogenic and non-oily agents should be used on acne-prone skin.
To sum it up, it is highly recommended that you use broad-spectrum, insect repellant sunscreen with no estrogenic effect so as to reduce the risk of breast cancer, and no fragrances or preservatives as they can cause allergies. It is also recommended to not use sunscreen on children less than 6 months of age. Proper application and re-application should be ensured for the maximum efficacy of an appropriate sunscreen.
Figure 2 – Biological changes observed in vitro in reconstructed model without or after UVA exposure. Oxidative stress was revealed by DCFH‐DA probe, fibroblast alterations correspond to apoptotic process (TUNEL reaction),and disappearance of dermal fibroblasts was revealed by histology (HES staining). Cell Death Differ 1998: 5: 792–802., .
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- Latha MS, Martis J, Shobha V, et al. Sunscreening agents: a review. J Clin Aesthet Dermatol. 2013;6(1):16-26.
- DeBuys HV, Levy SB, Murray JC, Madey DL, Pinnell SR. Modern approaches to photoprotection. Dermatol Clin. 2000;18(4):577-590.
- Giacomoni PU, Teta L, Najdek L. Sunscreens: the impervious path from theory to practice. Photochem Photobiol Sci. 2010;9(4):524-529.
- Medeiros VL, Lim HW. Sunscreens in the management of photodermatoses. Skin Therapy Lett. 2010;15(6):1-3.
- Matts PJ, Alard V, Brown MW, et al. The COLIPA in vitro UVA method: a standard and reproducible measure of sunscreen UVA protection. Int J Cosmet Sci. 2010;32(1):35-46.
- Marionnet C, Grether-Beck S, Seité S, et al. A broad-spectrum sunscreen prevents UVA radiation-induced gene expression in reconstructed skin in vitro and in human skin in vivo. Exp Dermatol. 2011;20(6):477-482.
- Battie, Claire et al. “New insights in photoaging, UVA induced damage and skin types.” Experimental dermatology vol. 23 Suppl 1 (2014): 7-12.
- Albrecht, S et al. “Skin type differences in solar-simulated radiation-induced oxidative stress.” The British journal of dermatology vol. 180,3 (2019): 597-603.
- Williams JD, Maitra P, Atillasoy E, Wu MM, Farberg AS, Rigel DS. SPF 100+ sunscreen is more protective against sunburn than SPF 50+ in actual use: Results of a randomized, double-blind, split-face, natural sunlight exposure clinical trial. J Am Acad Dermatol. 2018;78(5):902-910.e2.