I can see a thick zinc oxide paste being more persistent on the skin. But the maximum PPD of typical formulations will be about 1/4 of Dermo Peds. There is one exception, SVR 50B, it has a PPD of about 20. You could try that one on your nose, use something cheaper elsewhere.

I think you can find it for less $ than here.
http://www.beautyplatinium.com/product_p/svrs50.htm

Thanks for the recommendation. But is PPD 20 actually on the label or was it estimated?

It's a tested value.

I thought zinc oxide blocked more long wave UVA than titanium, and it has less zinc.

Depends on the particle size, the coating, and the carrier.

question, do you think it's a good idea to apply it over Anthelios xl or over another ss with avobenzone?

If they are both photostable, it should not be a problem unless there are weird film formers, which some of them do have.

I read that avobenzone and zinc oxide are not used together in ss for incompatibility reasons, but what if they are just layered, after one fully dries?

There may be some deactivation at the interface, but you'd need a lab to test it to find out how much.

But I wonder why a derm like Leslie Bauman claims that she layers sunscreens, since she thinks it's more protection.

She's not telling all of what she knows, more specifically the precise circumstances under which it's an ok thing to do. Y

For normal consumers it's not advisable. If you think you are not an expert, getting the highest PPD you can stand, applying it lavishly and reapplying it frequently with your 5" wide visor and sunsglasses would be more prudent than layering two different brands which may or may not be completely compatible.

kosmeds, what do you think about the CIBA sunscreen simulator and its accuracy when gauging PPD protections. I remember you saying something before about how particle sizes for physical sunscreens are not the same for each distributor so its near impossible to gauge the PPD protections, yet the ciba sunscreen simulator still manages to find out the PPD based on only the active ingredients and percentage of active ingredients. Do you think the numbers they generate are a good "ballpark" measurement?

For example, right now the sunscreen simulator says that when I apply my 22.5% zinc oxide sunscreen + 6% titanium dioxide sunscreen at about 3.0mg/cm^2, I am getting about 22.2 PPD protection, which is on par with a lot of those stronger European sunscreens with high PPDs. Do you think this is an accurate assessment of the PPD, give or take a few points depending on what ZO and T2O particle sizes are used? Honestly, I would love to switch over to using chemical sunscreens like the European ones but they are so expensive. If I can mimic those strong UVA protections with a physical sunscreen and more appliance than I'm willing to do that because my budget can't handle all those European sunscreen prices. The 22.5 ZO + 6% T2O sunscreen I use makes my face inappropriately white but I dust it over with the Physicians Formula bronzer which is very concentrated in titanium dioxide and a bit of zinc.

What do you use to protect your lips?

{when I apply my 22.5% zinc oxide sunscreen + 6% titanium dioxide sunscreen at about 3.0mg/cm^2, I am getting about 22.2 PPD protection}

That seems high to me. Previously the L'Oreal people found 20% ZnO gave a PPD of 3.1 while CIBA found 16% ZnO provided a PPD of 4.2 with no other filters present. But since micronized TiO2 provides little protection above 340 nm, it would not be expected to boost the PPD significantly. There might be film stabilizers in the formulation that bring things up a bit. But I'm skeptical. My guesstimate at 2mg/cm^2 would be around PPD 8.0.

I'd ask the manufacturer to be certain. They probably have done PPD testing, but it's not something they put on the label if they are sold in the USA. If you are persistent about talking to a technical person when you call customer service you might get a useful answer.

Are you really applying 3 mg/cm^2? At that rate it would look like a thick white paste even with micronized filters. That's more than 1/3 of a teaspoon. Most people apply 0.5-1 mg/cm^2. I guess I'd have to see it to believe it. I can do that when I am at home in my backyard but not when I am in public.

But yes, there are cheap sunscreens with high PPDs, the one I use now is $21 for 200 ml (as opposed to the usual 100 ml tube), SPF50+/PPD 24 on the label. That's still far less expensive than typical. I used http://pharmazon.gr

I think the simulator is ok for basic USA formulations that have no more than 2-4 familiar filters. But they are better for the Euro formulations. Sometimes they are way off for USA formulations since they don't have all the USA tweaks for PPD boosting. But they seem to be improving in accuracy.

Edited to add: also there are pretty big variations in protection action spectrum for TiO2 and ZnO depending on the particle size, the material in which it is dispersed initially (if any, some manufacturers use predispersed minerals), whether it is oil or water soluble, what type of coatings are present, and the size of the clumps of the particles as they cluster. All these things make it difficult to pinpoint the actual PPD without in vivo testing, and only 4 of all the possible mineral products available are incorporated in the Ciba simulator.

Most of the Euro LRP formulations contain TiO2 and they go on white, not clear. So you can tell if you have missed a spot. The whiteness fades as it penetrates the stratum corneum, though, takes 5-10 minutes for me unless I apply much more than 2 mg/cm^2 in which case I can still see it on my face for hours.

Awesome info, kosmeds! STICKY PLEASE!!

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Pay no attention to Caesar. Caesar doesn’t have the slightest idea what’s really going on. Kurt Vonnegut