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Shielded by Science: How SPF is Scientifically Effective

Apex, NC

Introduction

Summer has rolled around yet again this year, coming in hot along with lazy afternoons, sticky popsicle fingers, and weekends spent at the beach. And it’s all thanks to that glorious, glittering ball of heat basking the Earth in her warm glow–the sun. It may seem bright and beautiful, but sometimes under the summer sun, it might feel like you’re soaking up that good old vitamin D when in reality you're cooking like a turkey in an oven. That’s where our hero SPF comes into play. In this article, you’ll be learning how much the sun really affects the skin, what exactly SPF is, and how it scientifically saves you from toasting to a crisp.


What’s so harmful about the sun?


Cross-section of skin layers: epidermis, dermis, hypodermis. UV rays penetrate, sun above. UVA rays penetrate deeper than UVB rays. Labels in light blue, background blue.
An image depicting the difference in penetration between UVA rays and UVB rays.

So, what exactly is so dangerous about the sun? Sure, it hurts to look at for too long, but what’s it got to do with the skin? The main culprit behind the sun’s heat is UV rays. There are two different types of UV rays: UVA rays and UVB rays. UVA rays can penetrate deep into the skin and can break underlying blood vessels present in the dermis of the skin. They can also cause early signs of aging by damaging collagen and elastin in the skin over time, so all those expensive serums and K-beauty products you’ve been piling onto your skin nightly for months will end up being in vain. UVB rays, on the other hand, are shorter and only penetrate into the surface of the skin, but they result in more immediately observable damage. UVB rays are what cause sunburn, and they trigger direct DNA damage in cells. Both UVA and UVB rays, however, can increase the risk of skin cancer and mutate the DNA of skin cells. Both UV types also stimulate melanin, the biomolecules in your skin that are released when exposed to the sun for too long to absorb harmful UV radiation, giving you that beautiful tanned glow you killed your skin cells to obtain. 


What does sunscreen/sunblock do to protect you?


SPF, which is in all kinds of sunscreen or sunblock, stands for “sun protection factor”— I think you can guess the basics of what it does already. But to take a deeper dive into the science behind it, SPF protects your skin through either chemical filters, physical filters, or both, depending on the sunscreen. Chemical filters are absorbed into the outer layers of the skin and use organic chemical compounds to absorb UV radiation and convert them into a small amount of heat. That heat is then released from the skin, leaving you almost completely damage free. Physical filters stay sitting on the surface of the skin and fight UV rays by scattering and reflecting radiation away. Both chemical and physical filters are incredibly effective in keeping your skin safe from the sun. However, there are pros and cons that come with each type. Chemical sunscreens are lighter and less visible, meaning they aren’t very likely to leave a white cast and are easier to rub in, making them ideal for those who like to layer their sunscreen under their makeup. The downsides? Chemical filters take 20-30 minutes to really start to work, and they’re also more likely to cause irritation due to the harsher chemicals they contain. They may also require more frequent reapplication due to UV rays breaking down the ingredients. Moving on to physical sunscreens, this kind of sun protection starts working immediately, perfect for a scorching day at the beach. They’re also gentler on the skin and are less likely to cause allergic reactions. But physical sunscreens can leave a white cast or a chalky residue and may feel thicker or heavier on the skin. To tell if your sunscreen is chemical or physical, you can check the ingredients listed. Chemical filters often include avobenzone, oxybenzone, octocrylene, or other chemicals listed as the active ingredients. Physical filters will most likely include zinc oxide and titanium dioxide instead. 


What SPF should you use?


When looking at different sunscreens, you may notice different numbers on different products. Some sunscreens may read “SPF 30”, others may say 50 or even 70. So, which one is best for you? An SPF of 30 or higher is effective for most skin types, however, the fairer the skin, the higher the SPF should be. SPF 30 blocks about 97% of UV rays, and SPF 50 or higher can block around 98%. It should be considered, however, that many sunscreens can only shield the skin from UVB rays unless they are labeled as “broad spectrum” sunscreens, which help shield the skin from both types of UV rays. So for long days at the beach or tanning sessions at the pool, you should make sure your sunscreen is labeled right for maximum protection. 


SPF is essential for maintaining healthy skin and reducing chances of skin cancer. It’s like your skin’s bodyguard. It won’t stop the sun from throwing a punch, but it can shield you with science!




Works Cited


Harvard Health Publishing. “The Science of Sunscreen.” Harvard Health, Harvard Health Publishing, 15 Feb. 2021, www.health.harvard.edu/staying-healthy/the-science-of-sunscreen.

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University of Rochester Medical Center. “Sunscreens: Protect Your Skin.” Rochester.edu, 2024, www.urmc.rochester.edu/encyclopedia/content?contenttypeid=85&contentid=P01351.

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Thomme, Gina Van, and Kellie Bramlet Blackburn. “How Does Sunscreen Work? Understanding UV Protection.” MD Anderson Cancer Center, 18 June 2024, www.mdanderson.org/cancerwise/how-does-sunscreen-work.h00-159698334.html.

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NIH. “Sun and Skin.” NIH News in Health, 8 Sept. 2017, newsinhealth.nih.gov/2014/07/sun-skin.


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Written by Joy Sefein

Edited by Waverly S.

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