Seems to me like we should’ve easily invented something that lasts indefinitely by now
In: Chemistry
things in general have a hard time sticking to the surface of our skin. movement, sweat, ocean water tend to clear away most “stuff” that gets stuck or placed on skin
a sunscreen that lasted indefinitely would likely cause harm to your body by possibly blocking the natural exchange of heat and sweat
then there is the chemical component; of how long can the sunscreen last before being broken down by the very thing its protecting us from?? ever leave stuff out in the sun only to find it faded/melted or otherwise changed
Sunscreen absorbs intro the skin (albeit shallowly), and so will inevitably absorb out of the skin, additionally any on the skin will eventually be washed off.
Sunblock on the other hand stays on the outside of your skin and newly completely blocks any UV light, but can be easily rubbed off or washed off (think like the white zinc lifeguards apply to the nose).
We could create something (probably sunblock) that lasts significantly longer, but we’d (at the very least) have to make it not soluble in water, and not easily rubbed off (so sticking to the skin). So it would have to be removed with alcohol, acetone etc. which is not ideal. It would essentially be like a spray (or rub) on second skin that would be a pain to remove.
Most people wouldn’t want that, and would prefer the much easier option of just wearing clothes (or swimwear) that block out UV light well, this could be done very easily, as most clothes already block out a lot of UV (which is why people have “farmers tans”).
You can easily apply a substance to your skin to block UV, the problem is that anything that wouldn’t easily come off to last that long…wouldn’t easily come off.
The most effective, removable sun screen we have is clothing.
“Something that lasts indefinitely by now”
Like a hat? Or a shirt?
Any liquid is going to eventually evaporate. Even motor oil will evaporate if left out *eventually*.
Based on what?
If you’re not swimming or sweating profusely or putting sunscreen on @ 4am you will be perfectly fine.
What you’re doing while wearing sunscreen is what matters, not the chemical composition of sunscreen. Forget hours, if you go into the water you may need to reapply immediately.
Max efficiency != doesn’t work at all
Clothing lasts indefinitely and is pretty cheap. Works much better than the alternative of never ending chemical based sunscreen causing cancer or poisoning the body
It depends upon the sunscreen. Additionally, the US government doesn’t allow the better sunscreen protection and limits how long the manufacturer can state it lasts before needing re-application.
There are sunscreens that will last all day without reapplication and they used to be labeled as such. The FDA created new rules for labeling so manufacturers can no longer claim 24 hour protection. They still protect for 24 hours, however. The problem is, you don’t know which sunscreens those are. From my experience, they are typically the ones in the aluminum spray bottles that spray a fine mist. They stay on my skin for days and no amount of washing removes than. If I spray it on a Monday morning and I’m out in the hot sun all day Monday, Tuesday and Wednesday, I find that I’m still protected without reapplication.
I have very fair skin and without sunscreen, I’ll be red after an hour in the sun and I’ll be burned to a crisp within 2 hours in the sun so I can attest to the fact that these particular sunscreens do last a long time.
Have you tried Flex Seal?
No one has described the physics of how sunscreen works, and there’s a lot of misunderstanding on how sunscreen works in this thread.
Sunscreen gets absorbed into the skin (chemical) or sits on top of the skin (physical) The UV rays have a lot of energy that damages the skin which can lead to cancer, early aging, etc. When the UV rays encounter the sunscreen, the sunscreen absorbs the UV which photodissociates the chemicals in the sunscreen. This breaks the UV rays up into lesser energetic components that do not damage the skin. So by its very nature, sunscreen can’t last indefinitely because it’s not supposed to.
BOTH physical and chemical sunscreens work in this manner. It’s a myth that physical sunscreens reflect light.
Link to the study that shows physical sunscreen absorbs and doesn’t reflect: https://onlinelibrary.wiley.com/doi/10.1111/phpp.12214
Sunscreen is basically body paint, that either absorbs or reflects ultraviolet light. You can make it harder to wash or rub off, but you’re never going to make it permanent, because your skin isn’t permanent either.
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