Keep looking on the backside of any chemical based sunscreen tube and you’ll begin to notice that there are a limited number of chemical ingredients which are repeatedly used in varying % and cocktails across all sunscreen brands. I am by no means a chemist nor do I have a degree in any cosmetic related field. But I believe I can read and understand a dumbed down power point from people much smarter than me.

Why are there different chemical UV blockers used in sunscreen?

It basically boils down to the properties of the molecule/compound. When a scientist decides to make a sunscreen, they first ideate the use case then they select the desired properties. Based on the use case and desired properties, the ingredients are then selected.

The image below shows UV absorption profiles for common chemical UV filters. If say designing a broad spectrum sunscreen (in a perfect world), one would choose the desired wavelengths to block and then select the cocktail of UV blockers.

The problem is that it isn’t so simple to just pick and choose ingredients solely on UV blocking characteristics and mix them all together. Each one of those ingredients have other different physical properties which affect the way the sunscreen feels. Which brings us to the next question.

Why is there typically more than one chemical active ingredient in a sunscreen?

Peak UV wavelength properties are not all that is looked at when selecting a particular chemical sunscreen active ingredient. Some ingredients feel thick and greasy, cast a yellow tint to the mixture, and even don’t mix well with other ingredients. Ever try to mix oil and water together? The same principle is at play here.

Each UV filter comes with its own characteristics which can be a pro or con to the desired sunscreen use case.

Factor in costs, supply chain availability, health regulations, and market conditions, one can imagine the amount of consideration a sunscreen must go through when selecting just the active ingredients (not even factoring in the inactive ingredients)! So it is not unlike a witch brewing a magic potion. “A little bit of this, a little bit of that” to make a formula to have just the right characteristics per intended use case requires just the right amounts of multiple ingredients.

So what do we do with this information?

Honestly, I would leave those formulation decisions up to the sunscreen company who is producing the sunscreen. I’m sure they have big brains working on their magical sun protecting ultraviolet blocking potions. What I do glean from all this information however is to a varying degree, the coverage of the UV wavelengths I can expect to be protected from (I say expect because how they are implemented/mixed with the inactive ingredients will alter the final result).

If say you have a typical 3 ingredient chemical based sunscreen, say a lotion containing Avobenzone 3%, Octisalate 5%, and Octocrylene 10%. Knowing each filters blocking properties and critical wavelength helps establish the range of UV wavelengths the formulation effectively blocks.

Octisalate 5% – Critical wavelength of 327
Octocrylene 10% – Critical wavelength of 353
Avobenzone 3% – Critical wavelength of 383

So here you have the critical wavelengths nicely spaced to block from 327-383. Remember that UVA is UV wavelengths from 315nm – 400nm and UVB, the ultraviolet wavelengths from 280nm – 315nm. Given the 3 combined UV filters show blocking from 295nm to 383 (with wavelength filtering protection attenuating depending on UV filter), we can be assured there is some degree of protection at all wavelengths, with peak protection at those critical and peak absorbtion wavelengths.

So what now?

Easy. Just memorize the tables above and you’ll be set to analyze if the sunscreen is supposedly broad spectrum and at what wavelengths the most protection will typically be. Ha. But here’s the thing…even if you can memorize the UV filters, critical wavelengths, and corresponding peak absorbance data, you wont know how the sunscreen really performs until its tested, because the active ingredients are just one part of the equation.

Enter the sunscreen tester.

More Info

The window below contains the PDF where I got all this neat information. I got it from the FDA website, but its hard to find, so you can download it directly here.