The Chemists' Comprehensive Guide to Sunscreens Pt.1

First Posted on May 10, 2021 in:science deep diveskincare fundamentalssunscreen

Looking for a review on sunscreens?! Well look no further!

Summer is just around the corner and the skincare market is already starting to rollout with new sunscreen launches. On top of all this, sunscreens have recently been under a lot of scrutiny with all the recent SPF testing drama. That, plus the FDA blood stream study and coral reefs... this category seriously just can’t catch a break. So it's high time we updated our sunscreens guide. 

In this part I, we’ll go over the basic science of sunscreens and the current controversies and issues surrounding the category. In part II, we’ll focus on some strategies on just how to shop for them. So let’s get started with the biology!

The Biology: (Whenever you need another reminder of why you should sunscreen)

sunscreen UV skin diagram

The sun emits two types of UV that cause skin cancer and photoaging, UVA & UVB. UVB is the shorter wavelength mainly responsible for sunburns and most skin cancer. UVA is the longer wavelength that’s able to penetrate glass and is mainly responsible for generating free radicals in skin that leads to indirect DNA damage and photoaging. The term ‘photoaging’ was entirely created for the sheer impact sun has on skin since UV damage results in leathery texture, premature wrinkles, dullness, and hyperpigmentation. “SPF” value describes the level of UVB protection you’re getting, whereas labels such as “broadspectrum” and “PA++” are describing UVA coverage.

Sunscreen Science

Sunscreens can be divided into two categories based on their filter type. Both chemical and mineral filters for the most part work the same way. To protect your skin, these filters absorb these UV rays and dispelling that energy as heat.

Chemical Filters: Can also be referred to as organic sunscreens. The naming scheme is all sorts of confusing because technically all formulas, whether chemical or mineral sunscreens are ‘chemicals’. They’re sometimes referred to as organic sunscreens because these filters are carbon-based not because they have anything to do with agriculture concerns. Unfortunately… this is where most of the sunscreen controversies come from.

  • SPF Value Concerns: Recently there have been several brands that have reported significantly lower values than claimed. It creates a lot of doubt and skepticism in what sunscreen you're buying, but there’s a couple things to keep in mind.
    • Why is it happening? Hear it from a chemist, sunscreens are tricky formulas that degrade easily. There are so many factors that can attribute to SPF value including the other ingredients in the formula, the packaging, the formula structure itself. To make it even more difficult, SPF testing and validation is expensive. So for many products, only one test is conducted, which means it’s sadly not very surprising that some of these SPF values are less than originally claimed. These two factors combined It’s the reason why we still haven’t come out with our own sunscreen. Donations anyone?
    • How do I put my mind to ease? The reality is, the sunscreen category is where you want to shop for bigger brands for the most reliability. Old timers such as La Roche Posay, Shiseido, Biore just have more experience and a bigger budget to test their sunscreens in all sorts of different scenarios to ensure the most reliable performance
  • Coral Reef Concerns: A couple years ago, studies showed that chemical filters like octinoxate and oxybenzone caused coral bleaching and impacted young coral development. Sunny getaways such as Hawaii and Florida both ended up banning the sales of chemical sunscreens with oxybenzone and octinoxate. Except, it turns out those studies didn’t quite use real world scenarios, testing ~10x the concentration of sunscreen filter that realistically would be found in the ocean. What does it mean? While more studies are being conducted to test under more realistic standards, we understand and appreciate the care for our ocean life. So it doesn’t mean we should ban octinoxate or oxybenzone completely, but we can understand the sentiment to use mineral while doing some ocean snorkeling.
  • FDA Bloodstream Study Concerns: The FDA recently shared results of a clinical where they found concentrations of chemical sunscreen filters in the bloodstream to be higher than the allowed safety limit. Long story short, a lot more studies are needed to understand what this all means since the safety limit value is an incredibly conservative and generic value given for all ingredients. At this point in time, no reasons have been given to doubt chemical sunscreens and ultimately skin cancer is still the real evil here. Additionally these filters have been under scrutiny for decades, so we’re not that worried about these findings until more research has been done.
  • Characteristics (finally some good news!): Probably the reason why chemical sunscreens have been so controversial is because we just can’t live without them despite all the press they keep getting. These formulas have a significantly better texture and finish than minerals that make them ideal for good sunscreen habits , layering and general ease of use especially for combo, oily, and acneic skin types. 

Mineral Filters: Can also be called physical or inorganic. There are just two ingredients in this category - titanium dioxide and zinc oxide. There's been a recent buzz around minerals with their claim to fame being that they're more gentle. But are they actually better for sensitive skin types? Because these are inert powders, we do recommend mineral sunscreens for very sensitive skin types that have really struggled with chemical sunscreens.

  • In the EU and Asia, there are more nano options of these mineral filters. If you do a quick google of nano sunscreens there’s quite a bit of fear around nano but know that there isn’t any evidence that the nano form is less safe, and can be a beneficial option for oily skin types since they can provide a lighter texture and minimal white cast.
  • Characteristics: There's a major tradeoff with minerals and that's texture. These usually end up being a much heavier formula that has a tendency to leave a white cast. Brands will tint them to minimize the white cast effect but still these are generally not ideal for darker skin tones.

Sunscreens & US Regulatory

A thorn in our side regarding US Sunscreens is our very own FDA. Unfortunately getting any sort of new sunscreen filter approved is painstakingly slow. (we’re talking decades at a time) and sadly our sunscreen library is both limited and slightly outdated. 

Additionally, our UVA claims aren’t great either. To claim UVA protection in the US, it’s a simple pass/fail “broadspectrum” label. Brands can achieve this claim via an in vitro test of 5 measurements showing that 90% of the UVA falls under the critical wavelength of 370nm. While this saves brands a significant amount of money in testing, this sort of pass/fail metric doesn’t give us the best picture of the amount of UVA protection the user is getting. One note of comfort is that brands are acknowledging this lack of transparency, and you’ll find some brands recently adopting Asia’s PA+ testing method for better indication of UVA protection.


  • For proper sun protection and UV damage, sunscreens need to have both UVB and UVA protection.
  • You can divide sunscreens into two categories, chemical and mineral sunscreens.
  • Chemical sunscreens have been under some scrutiny but this doesn’t mean that you should eliminate these from your shopping choices since they can provide better textured formulas that promote better sunscreen habits.
  • Checkout some of our favorites and our community's favorites here
  • Part 2 coming next! How do you shop in such an important yet complicated category?


Schneider, Samantha L., and Henry W. Lim. "Review of environmental effects of oxybenzone and other sunscreen active ingredients." Journal of the American Academy of Dermatology 80, no. 1 (2019): 266-271.



chemist confessions sunscreen pt 2 banner image

The Chemists' Comprehensive Guide to Sunscreens PT. 2

By now, hopefully we’ve given you a general idea of why you should use sunscreen (premature aging and skin cancer! do we need to say more?!) and are up to date on sunscreen news (chemical sunscreens could use some PR help). Now that you have a sense of the state of the sunscreen world, let’s get to the good stuff and talk products and how to pick your next winning sunscreen sidekick! Step 1: You feeling Chemical or Mineral? The category is vast, confusing, and keeps adding new launches. It do...

Read more
Sunscreen Challenge

Results Summary for our 2023 30-for-30 Sunscreen Challenge

In celebration of summer, we decided to test 30 different sunscreens over 30 days to see how these applied, how they held up over time, and even how they wash off. Please head to our TikTok and Instagram channel if you want to see the visuals. Otherwise here’s the running list of sunscreens we’ve tried, our rating, and why: *To help readers learn more about products showcased in this challenge, we built out and organized these results in Shop My Shelf. We do receive a small commission for usi...

Read more