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Comment by axpy906 | Hacker News Reader

Got to watch out with sunscreen too. Many brands have ingredients that can pass the blood brain barrier.

Shit like what??

Zinc oxide and titanium dioxide are the only two sunscreen ingredients the FDA considers truly safe sunscreen ingredients, and as someone with a basic understanding of biology, I tend to agree with them on this (1). Zinc oxide and titanium dioxide nanoparticles refuse to penetrate the skin even when rubbed into open wounds and they have negligible effects in vivo when used topically. Additionally and crucially they block UVA, the major skin cancer promoter, which won't give you sunburns. Zinc oxide is the most effective broad spectrum sunscreen. Titanium dioxide is less effective with UVA absorption. All other sunscreen compounds function after being absorbed into the skin. Unfortunately they also get into the bloodstream where they act as hormones such as estrogen mimickers (unintentionally).

The only downside of zinc oxide and titanium dioxide is that they are awful to apply (you need a good technique) and you will probably look awful after application. It may be better to apply less material at a time but more often. Most manufacturers recommend every 80 minutes. I think this is defined by FDA regulation.

Since zinc oxide and titanium dioxide are semiconductors, they can both reflect and absorb UV. I think there is a large gap in understanding by sunscreen manufacturers of how these nanoparticles perform on a quantum level. I hold out hope that some chemist can further engineer these nanoparticles perhaps through an innovative coating to further improve performance and appearance when applied. I think there is still a lot of money being left on the table and these compounds are under appreciated, not understood well, nor developed enough to this day. Fortunately the sunscreens containing them do work today.

[1] https://www.fda.gov/media/153964/download

I mostly use zinc oxide sunscreen and don't think I look awful, which I understand is both a personal opinion and also something that can vary from person to person based on skin tone.

I think they’re referring to the white overtone that zinc based sunscreen leaves due to poor absorption

That's what I thought, too.

I mean, just google "Zuckerberg sunscreen".

Of all the metalic elements, Zinc is relatively harmless and actually has been shown to inhibit the process of viral replication.

By the way no one knows how elements behave on the quantum level we don’t have a quantum computer nearly powerful to simulate anything more than hydrogen

There are some relevant effects of UV on these semiconductor sunscreens to consider. For example:

It is generally agreed that UV absorption excites an electron from the valence band to the conduction band of the semiconductor. The resulting excited electrons, in the otherwise empty conduction band, and the “positive holes” in the valence band allow charge transfer to the TiO2 surface which facilitates oxidation of surrounding molecules. Sometimes direct charge-transfer causes the oxidation.

https://www.mdpi.com/1420-3049/19/11/18192/htm

Some questions which stem from this finding include: what is being oxidized on the skin in its immediate vicinity when UV makes contact with the semiconductor sunscreen? What are the implications?

Is there any performance difference between nanoparticle sizes?

So has water

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