I have a question regarding the protection Uvinul A Plus offers

 …on Wiki and in a BASF PDF, I see it listed as having peak protection ~350 nm. This means it protects in the UVAI part of the spectrum. However, skinacea lists it as protecting from UVAII (which it still does cover). Does this imply that it’s inadequate in UVAI protection? Also, how weary should I be of the BASF ppd estimator? There are some Ombrelle sunscreens I want to try, but no labelled ppd (I wish they’d use ppd 🙁 ). Thanks!

Hi battleofthe-s,

Protection offered by sunscreens occurs on a curve, UVA II is 320 to 340 nm and UVA I is 340 to 400nm.

While the peak of Uvinul A Plus (DHHB) is in the 350nm region, it still offers protection in the 320 to 340 nm area. As well as beyond the 350 nm peak.


UVB sunscreens also tend to extend into the UVA I region, and since most sunscreens contain a mixture of UVA and UVB filters, you should be well covered.

However, there is a lack of sunscreens that have a peak in the 320 nm to 340 nm range, and there are newer ones being developed to target that area – unfortunately they don’t have approval anywhere yet.

The BASF Sunscreen Simulator is for formulation use only. The only way to know the UVAPF or UVB protection offered by a sunscreen is to test it on a human panel, or in vitro for UVAPF (COLIPA Method).

You can have two identical sunscreens, but due to differences in production have an SPF of 5 or 50. The distribution of sunscreen chemicals in the product is really important for sunscreens, as well other ingredients can increase or reduce the efficacy of a sunscreen.

Unfortunately the simulator can’t account for those.

Hey there, thanks for the resource. Do you happen to know if using a facial oil with occlusive properties (passionfruit oil, in my case) interferes with a physical blocker sunscreen?

Hi theaomai, thanks for the question!

There’s a misconception that sunscreen needs to “bind” with your skin cells in order to activate protection. This is a myth for both physical (inorganic) and chemical (organic) sunscreens. 

The chemicals themselves absorb the UV wavelengths, not the skin cells – what’s important is that the sunscreen is able to form an even layer on the skin. 

Too much oil on the skin, could prevent a sunscreen from forming an even layer, just by virtue of being greasy and by preventing the sunscreen from drying or applying smoothly. Same goes with wet skin. 

If you can still move the sunscreen on the skin after you’ve applied it, that means over time gravity will pull more sunscreen into the crevices of your skin – making the sunscreen coverage uneven. Not to mention it’ll be more easily wiped off!

I would recommend gently blotting any excess oil off the skin before applying your sunscreen.

Hope that helps! 

Dear Stephen, thank you for answering my last question! I have another. Can you explain why some skincare topicals are available only by prescription while others are available OTC?

For example, why does tretinoin cream require a prescription while retinol does not? I realize the easy answer is because “the FDA says so,” but I don’t really understand how one could abuse tretinoin, even though it is more potent, and so I don’t understand *why* the FDA says so. Lobbying? Patents? Random? Thanks!

Hi Jechristine, sorry it’s taken so long to get to these questions!

This is a great question and what you need to look at is the regulations of what the FDA considers a “cosmetic” vs. a “drug”.


The main thing that differentiates the two is the claims that the product can make. For example tretinoin can claim to treat acne as well as photoageing.

Even though retinol is a similar compound and may have similar effects as tretinoin, can’t claim the same. This is because retinol hasn’t been submitted for drug approval.

If a company wants to make claims like treating acne or treating photoageing for a retinol product, they’d have to submit it as a new drug. This would involve conducting human clinical trials to establish efficacy and data, just like any drug the FDA considers for approval. This is a lengthy and costly process.

Keeping to acne treatments, benzoyl peroxide, salicylic acid, and sulfur are approved by the FDA to treat acne. An over-the-counter product with these active ingredients can make the claim that it treats acne. Other acne treatment ingredients without FDA approval can only allude to treating acne, but can’t directly claim it.

This is why a lot of the marketing copy on cosmetics are very flimsy or elude to a treatment. “Purify skin” vs. “Acne treatment”.

This isn’t just for cosmetics. For example, you have prescription fish oil supplements and over-the-counter ones. The company manufacturing the prescription fish oil supplements submitted it as a new drug, and went through the process to get it approved as a treatment for a condition. They can make claims that over the counter fish oil supplements are unable to.

Under the FDA regulations any cosmetic that claims to alter or change the functioning of the skin, treat or cure a disease, or provide photoprotection is no longer a cosmetic – but a drug, and requires all the clinical trials and approval that any other drug would require.

Not all companies follow these regulations and you do see products that imply that they change the way the skin functions. It’s a blurry line, and a lot of these products get a pass. Not because the FDA approves them, but because the regulations arm of the FDA is probably underfunded.

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Dear Mr. Ko, Could you offer your professional opinion of comedogenic scales

like those used by CosDNA? Have these been discredited, or is there something to them? I see lots of people attempting to single out and eliminate specific acne “triggers” — i.e. specific troubling ingredients — and I’m wondering if so doing is a fool’s errand? What do you think?


CosDNA doesn’t list their sources (to my knowledge), but comedogenicity data is generally performed on rabbits, or rabbit ears specifically.

A high % (50% to 100%) of the ingredient is placed on the ear for a period of time and then monitored for comedones. Sometimes the ingredient is injected under the skin.

Researchers started coming to conclusions that moved them away from using these 1 ingredient animal results.

Firstly, while rabbit ears easily form comedones, they don’t correlate to human skin.

And secondly, using 1 ingredient in a high concentration doesn’t reflect its use in a consumer product.

Human sebum, for example, is very comedogenic. But it doesn’t cause problems for everyone.

My personal opinion is that the melting point of an oil or wax is more indicative of whether it will cause clogs or not. If your skin is warm enough to melt it, it’ll remain in a more fluid state, and less likely to clog pores.

It gets more complicated when you consider irritancy of an ingredient as well. While an ingredient might not be pore clogging, if it can cause enough irritation it may cause already formed microcomedones or comedones to erupt into inflammatory acne. This sometimes gets characterized as “purging”, especially common with prescription retinoids and chemical peels.

Hope that helps!