<story><title>After two hours zinc oxide sunscreen loses effectiveness, becomes toxic: study</title><url>https://phys.org/news/2021-10-hours-sunscreen-zinc-oxide-effectiveness.html</url></story><parent_chain></parent_chain><comment><author>drcode</author><text>Putting together all the messaging I&amp;#x27;ve gotten recently: Regular sunscreen is bad, zinc oxide sunscreen is bad, getting sun is bad, not getting sun is bad (Vitamin D).</text></comment>
<story><title>After two hours zinc oxide sunscreen loses effectiveness, becomes toxic: study</title><url>https://phys.org/news/2021-10-hours-sunscreen-zinc-oxide-effectiveness.html</url></story><parent_chain></parent_chain><comment><author>at_a_remove</author><text>As someone with a severe photosensitivity disorder, I have relied on zinc oxide as a &amp;quot;physical&amp;quot; blocker as opposed to various chemicals that often seem to be banned in the EU.&lt;p&gt;But digging into the article, which is a little short on specifics, it appears that the zinc oxide is catalyzing a reaction with the &amp;quot;organic&amp;quot; compounds which &lt;i&gt;also&lt;/i&gt; are blockers.  Zinc oxide is already a pretty good UVA blocker, especially with a smaller particulate size.  My guess is that this is for sunscreens with a mix of organic UVA blockers and zinc oxide, but not so much zinc oxide that you look like you are training for mime school.&lt;p&gt;My preferred (aka &amp;quot;least objectionable&amp;quot;) blend is only zinc oxide, so I may not have to worry.&lt;p&gt;I wish I had access to a UV-VIS spectrophotometer and various defined particle sizes of zinc oxide and titanium dioxide.  My suspicion is that a careful formulation -- probably arrived at via linear algebra -- of different particle sizes should allow for a sunscreen that almost has a step function at around 410 nanometers: invisible at longer wavelengths, a complete block at anything shorter than 410 nm.  This way, one could avoid the ghost whiteness.</text></comment>