The truth about SPF

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The warmer seasons are upon us and I can't wait, mainly because it's my birthday season in spring. However, with temperatures rising, we are going to be seeing Mr.Sun a lot more and it is extremely important to understand how sun protecting factor (SPF) works and the difference between UVA, UVB, and UVC rays. This knowledge will hopefully ensure you make informed decisions when purchasing your sunscreen.

What are the different types of Ultraviolet Radiation? 


Ultraviolet radiation has a broad spectrum which ranges from 40-400nm.  It comes just before visible light on the electromagnetic spectrum.

UVA has the longest wavelength (400 nm - 320 nm) and is able to penetrate the ozone layer and into the skin.  This radiation tends to result in wrinkling, speeding up the process of ageing (photoageing), and dulling the skin.  Photocarcinogenesis can also result due to direct damage to cells and deoxyribonucleic acid (DNA).  This can result in mutations in human menalocytes that can result in skin tumours or cancers. (3) UVA has been said to up-regulate matrix metalloproteinase (MMPs) formation which are enzymes that degrade collagen and elastin in the matrix.  Therefore, it reduces the skin's elasticity and smoothness, results in wrinkling, and lack of firmness. (2)

UVB (320 nm-290 nm) is not completely blocked by the ozone layer, despite having slight wavelength overlap with UVA.  Exposure to UVB can result in pigmentation, discoloration, sunburn, photocarcinogenesis, inflammation, and also immune-suppression. (2)

UVC (290-220nm) is completely blocked by the ozone layer, therefore is not a threat unless you are in an environment with extreme UVC exposure such as tanning salons/beds. (1)

How does sunscreen work? 

A majority of sunscreen agents contain titanium dioxide (TiO2), kaolin, zinc oxide (ZnO), magnesium oxide, calcium carbonate, and talc.  They work either absorbing, reflecting, or scattering the UV rays to prevent penetration into the skin.  The topical creams act as a physical barrier.  Most sunscreens do not have a shelf life of more than 3 years but in hotter temperatures and storage places, this can significantly decrease.  Always use in-date sunscreen.  (4)  The sunscreen should effectively block BOTH UVA and UVB rays.  Ensure that the sunscreen you invest in is broad spectrum sunscreen.

What is SPF?

SPF is Sun Protecting Factor used for protecting the skin and body against UVB rays.  It is measured using the following equation:
The Minimal Erythemal Dose (MED) is the amount of UV radiation that will cause minimal erythema in an individual's skin within a few hours of exposure.  Erythema is also known as sunburn. (5)  Therefore, if you apply a product that has SPF 20, the skin is protected until exposed to 20 times more UVB radiation than that is required to burn the protected skin.  Another way to look at it is: 


Therefore, if it takes you 20 minutes to burn in the sun without sunscreen, and the SPF suncream you use is SPF 10, it will take you 200 minutes before you burn in the sun.  Theoretically, after 200 minutes you should reapply your sunscreen.  Do bare in mind, many studies have highlighted the difficulty in formulating an appropriate and accurate equation.  Currently, there is no true measure of how much SPF can really protect you and how much cream is needed to ensure you have created a good barrier.  

All in all, make sure you do cover every inch of your skin and apply the sunscreen in accordance to the SPF number.  It won't hurt to over apply and put on twice as much considering the fact that most individuals do not use enough anyways.  

I hope this was a fun and informative read for you all! I really enjoy writing more science-y based posts and makes me feel like I am utilising my degrees more and it is very satisfying. 

1. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3543289/
2. https://www.ncbi.nlm.nih.gov/pubmed/11059365
3. https://www.ncbi.nlm.nih.gov/pubmed/11312434
4. https://www.ncbi.nlm.nih.gov/pubmedhealth/PMHT0025486/
5. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3734971/
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