Thread

The UV index is not the warm sensation of sunlight on bare skin

99 points · 79 comments · evakhoury

nomel · 1790116546 · focus · HN ↗
I don't know about this. I can feel where there are holes in my sunblock (which only block UV) which lets me know where to apply it, and the sensation is not one of heat of the sun, it's different. I'm not sure about the mechanism, but the presence of the sunblock stops the "UV" type sensation. This from the moment I put it on to long after the water component of the sunblock has evaporated. And, the type of sunblock doesn't matter (the drier waterproof kind or various lotion varieties). And, I do notice a difference between the different SPF, along with some "bad" sunblock that I just kept applying but couldn't make the feeling go away (it had apparently separated, and everyone that used it was burned).
I think the "real" test would be to just shine a UV light in a dark room, to see if the source can be identified while blindfolded, or something.
1. samusiam · 1790127275 · focus · HN ↗
  After you sure that isn't because your skin is moist where sunblock was recently applied, and therefore cooler?
  1. esseph · 1790131452 · focus · HN ↗
    Sunblock is supposed to reflect UVA/UVB, but doesn't do much for infrared or visible light, which is why your skin gets warmer.
    (Edited, fixed)
    jrochkind1 · 1790132295 · focus · HN ↗
    Sunblock is not supposed to reflect heat (infrared). It's supposed to reflect UV. Different spectrum. Kind of the whole thing the OP was about. I have no idea if sunblock also reflects infrared though, incidentally.
    <a href="https://care360.basf.com/emea/en/industries/personal-care/core-competencies/all-about-sun/sun-protection/how-do-they-test-a-sunscreen-s-protection-factor" rel="nofollow">https://care360.basf.com/emea/en/industries/personal-care/co...
    dreamcompiler · 1790175198 · focus · HN ↗
    Sunblock mostly absorbs UV (and turns it into heat). Some reflection occurs but it's mostly absorption.
    esseph · 1790181435 · focus · HN ↗
    After looking into this even more, there are two types:
    Mineral - Reflects
    Chemical - Absorbs
    dreamcompiler · 1790185349 · focus · HN ↗
    I thought so too but it's not the case. Even the mineral sunscreens mostly absorb.
    <a href="https://cen.acs.org/business/consumer-products/What-in-sunscreen-and-how-does-it-protect-your-skin-from-the-sun-rays/99/i27" rel="nofollow">https://cen.acs.org/business/consumer-products/What-in-sunsc...
    nomel · 1790194493 · focus · HN ↗
    Video with a UV camera is interesting: <a href="https://www.youtube.com/watch?v=E9tEEDpeJoo" rel="nofollow">https://www.youtube.com/watch?v=E9tEEDpeJoo
    Black means absorbed, of course.
    nomel · 1790276573 · focus · HN ↗
    And, omg, you can buy an active version on amazon, for this exact purpose: sunblock coverage check!
    <a href="https://www.amazon.com/s?k=uv+mirror+for+sunscreen+test" rel="nofollow">https://www.amazon.com/s?k=uv+mirror+for+sunscreen+test

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