I have been religiously devoted to sunscreen since I was very young; it started off as a desire to mimic my own mother’s skincare routine, but then I came to understand the importance of applying sunscreen daily: to prevent skin damage from UVA and UVB rays from the sun. The UV rays penetrate the skin: UVB rays promote cell proliferation that thickens the skin and UVA rays denature collagen fibers in the skin dermis, resulting in decreased elasticity and – gasp! – wrinkles.

Now that is super important but I’m also pretty vain, so it took me a very long time to find a sunscreen that both protected me and didn’t leave a pasty sheen both in photos and in real life.

 

But behold! I finally found my holy grail two years ago:

And now I look like this:

And here’s why! It’s a little thing (quite literally) called a nanoparticle: in this case, zinc oxide and titanium oxide, the primary compounds filtering against UV rays, are put into sunscreen product in nano-size form. Because it’s so small, the powder in the sunscreen liquid product is essentially rendered transparent on the skin upon application and voilà, no pasty sheen.

This makes sense because the nano-size is not visible to the naked eye; the nanoparticle can be up to 7500x smaller than the width of a hair. So how can a small particle be so effective? Here’s how:

Size and Shape.

Size and shape matter because the efficacy of SPF depends on them. Smaller = better SPF, but worse UVA protection. Manufacturers have to find the balance between these two considerations. As a result, the zinc oxide used in sunscreens is larger and provides greater UVA protection than titanium oxide products that appear clear on the skin. The sunscreen I use has both zinc oxide and titanium oxide, albeit zinc oxide in a greater concentration:

 

The shape and size of the particles affect sun protection. The smaller they are, the better the SPF protection and the worse the UVA protection. Manufacturers must strike a balance: small particles provide greater transparency but larger particles offer greater UVA protection. The form of zinc oxide most often used in sunscreens is larger and provides greater UVA protection than titanium dioxide products that appear clear on skin.

People were concerned that the small size meant that the particles could penetrate through the skin barrier and get into the bloodstream, which is toxic in large doses. However, as this study from 2016 states, nanoparticles are safe for use in sunscreens, as they don’t penetrate the skin and any zinc found in the bloodstream was likely in ionic form, which is physiologically normal. It is important to consider the use of nanoparticles in spray sunscreens when considering the risk of inhalation, resulting in zinc getting trapped in the lungs – that’s why this hasn’t been approved for use yet.

And what about the chemical nature of zinc oxide and titanium oxide when exposed to sunlight? These compounds are photocatalysts; they can form free radicals that damage surrounding cells when exposed to sunlight, and smaller sizes are more affected by UV rays.

But manufacturers have found a solution, and it’s one of my favorite things about using nanoparticles: surface modification! That’s right, we can coat the surfaces of these nanoparticles to dramatically reduce the potential for photoactivity, with data suggesting as much as a 99% reduction.

So next time you slap on some sunscreen (which I hope you do every day!!), know that this is actively happening:

Look at those nanoparticles working so hard! They keep me so young.

sources: 
https://www.ewg.org/sunscreen/report/nanoparticles-in-sunscreen/#.W61SXhNKg1g

https://www.sbs.com.au/topics/science/fundamentals/explainer/whats-deal-nanoparticles-sunscreen