I get asked a lot if I make a sunscreen product. I don’t. I’ll tell you why.
How Sunscreens Work
Most commercial sunscreens contain synthetic, non-mineral active ingredients like oxybenzone, octinoxate, and octisalate.
They work by penetrating the skin and then chemically absorbing UVA and UVB rays so that your body doesn’t absorb them instead. This is why these are called “chemical sunscreens.”
A big knock against these ingredients is they spur the growth of free radicals in the body, and can lead to developmental and reproductive toxicity.
Most mineral and/or “natural” sunscreens rely on zinc oxide as the active ingredient.
While zinc oxide is a mineral, it occurs extremely rarely in nature. The zinc oxide that’s available commercially is created by using zinc that’s been mined, and then distilled and purified to produce zinc oxide. 
Zinc oxide works by physically blocking or reflecting UVA and UVB rays. Sunscreens with zinc (or titanium) oxide are called “physical sunscreens” for this reason.
Zinc oxide does not get absorbed by your body. Even nano-particles, which are small enough to penetrate the stratum corneum (the outermost skin layer consisting mostly of dead cells), cannot penetrate any farther than that. 
This makes zinc oxide a much better choice for sunscreens, as its only real drawback is that it might leave a while, chalky film on your skin. (Remember, this is the physical barrier that is doing what you want a sunscreen to do: Block the rays without invading your body.)
So why don’t you make a sunscreen?
Sunscreen ingredients are classified as over-the-counter drugs by the FDA. This means that only approved drug manufacturers can sell sunscreen, even sunscreens that use zinc oxide as their active ingredient. I am not a drug manufacturer, and so I cannot sell sunscreen.
That said, zinc oxide is readily and legally available to anyone. And I’ve tried, over and over and over again, to formulate a zinc oxide-based sunscreen, even just for my family (since I can’t sell it).
It’s nigh impossible.
Zinc oxide is incredibly difficult to blend into anything else. The powder particles are electronically attracted to themselves, and so they seek each other out and ball up like, I don’t know, really sticky bally things. Even when I think I’ve thoroughly blended the ZO into a base within an inch of its life, in a couple days, it’s either balled itself up again, or else separated out.
Further, sun protection is a pretty damned important thing. Unless I’m positive that what I put on my family is going to protect them, I’m not going to put it on them. The risks are too great.
It turns out that even professional cosmetics manufacturers have the same problem.
There are endless recipes on the internet for “homemade sunscreen.” I’ve tried ‘em. Even on the good days, when I can get the batches to stay blended, I know that their effectiveness is questionable at best.
The Bottom Line
It takes professional, trained experts who use extremely expensive equipment and well-proven techniques to make effective sunscreen. Simply adding zinc oxide to lotion doesn’t do what you hope it’s going to do. In fact, it might even be harmful if you spend time in the sun unprotected.
I have yet to find a physical (“natural”) sunscreen I love. When I do, I’ll update you.
Do you have a physical sunscreen you love?