| ▲ | Nursie 4 days ago |
| Yeah it’s not really enough. The actual difference between (say) SPF 30 and 50 is not a lot, 96.7% UV filtering vs 98% but I’m not 100% sure how that translates to actual rates of cancer. However the worst offenders in the testing advertised SPF 50 but delivered SPF 4 (~75% AFAICT) |
|
| ▲ | andreareina 4 days ago | parent | next [-] |
| You can't compare the straight percentage, a 98% filter lets through twice as much as a 99% filter. |
| |
| ▲ | jandrewrogers 3 days ago | parent | next [-] | | In both cases though the level of UV will be easily tolerated, which is the entire point. UV index is a linear scale, so more SPF has rapidly diminishing returns even in places with a UV index of 15+. That the duration of protection is independent of SPF makes this particularly true. There are only a handful of places in the world where atmospheric conditions might give a very high SPF marginal benefits. | |
| ▲ | Nursie 4 days ago | parent | prev | next [-] | | True, so the important factor is - how does this map to your chances of getting skin-cancer? | | |
| ▲ | DoctorOetker 3 days ago | parent [-] | | The most reasonable answer is to look at the transmission percentage, not the blocking percentage. | | |
| ▲ | aydyn 2 days ago | parent [-] | | No it isnt. Two photons is twice as much transmission than one photon, but both cases are totally insignificant. |
|
| |
| ▲ | Thaxll 3 days ago | parent | prev [-] | | How? Sorry I'm confused by that statement. | | |
| ▲ | daemonologist 3 days ago | parent | next [-] | | If you have a "100 unit" light bulb, and a material that blocks 98% of the light it emits, 2 units of light are getting through. If you have a material that blocks 99% of the light, only 1 unit - half as much - is getting through. (This is why the SPF scale is inverted/measures transmittance. SPF 50 sunscreen theoretically allows through 1/50th of the UVB radiation (or whatever wavelengths are specified by your local regulator).) | |
| ▲ | rrsp 3 days ago | parent | prev [-] | | 98% = 2 units of UV reaching the skin 99% = 1 unit of UV reaching the skin Thus 98% filtering lets in 2x as much as 99% filtering |
|
|
|
| ▲ | cyberax 3 days ago | parent | prev | next [-] |
| > The actual difference between (say) SPF 30 and 50 is not a lot, 96.7% UV filtering vs 98% but I’m not 100% sure how that translates to actual rates of cancer. Counterintuitively, higher SPF matters a _lot_. The difference is in the _durataion_ of the protection and in the amount of sloppiness you can afford while applying the cream. Suppose that for you the half-life for the sunscreen is 1 hour. SPF 30 cream would thus decay to SPF 7 in 2 hours, providing little protection. But an SPF 90 cream would still offer quite reasonable SPF 25 protection. The same applies to sloppiness. SPFs are measured in perfect conditions, with a prescribed amount of the cream spread evenly. So the higher the SPF, the more mistakes you can make while applying it. |
| |
| ▲ | Ekaros 3 days ago | parent [-] | | Would different SPF sunscreens have same half-life? I have not dig into it, but I would think there is a few mechanism or chemicals and those would have different halflifes. | | |
| ▲ | cyberax 3 days ago | parent [-] | | Certainly, but the same principle still applies. Higher SPF will provide more headroom for a given chemistry. |
|
|
|
| ▲ | dylan604 4 days ago | parent | prev [-] |
| But what about the sunscreen with ingredients that are carcinogenic before you even need to consider UV protection? |
| |
| ▲ | XorNot 4 days ago | parent | next [-] | | Yes that would be serious so I suppose in an actual specific case regarding some specific real ingredients in products, we could discuss that. | | |
| ▲ | jonahhorowitz 3 days ago | parent [-] | | There have been cases of benzene being detected in sunscreen. It's not an intentional ingredient, just one that is common in industrial manufacturing. I don't think that's what the parent was worried about though. https://www.ewg.org/sunscreen/beware-of-benzene-shining-a-li... | | |
| ▲ | dylan604 3 days ago | parent | next [-] | | No, benzene was specifically what I was thinking of to the point that I assumed it was so well known that it wasn't question as being a thing any more. Just like asbestos in baby powder | | |
| ▲ | Nursie 3 days ago | parent [-] | | That’s thankfully no longer really a thing - the world has realised that there is no such thing as asbestos-free talc, so baby powder is now mostly corn-starch AFAICT. | | |
| ▲ | dylan604 3 days ago | parent [-] | | You mean in the US, right? Because J&J were known to continue to sell their talc based products internationally. | | |
| ▲ | Nursie 3 days ago | parent [-] | | It’s certainly stopped here in Aus too, and there was a UK documentary about it a while ago implying it’s known there as well. Beyond that, no clue. |
|
|
| |
| ▲ | dzhiurgis 3 days ago | parent | prev | next [-] | | If you drive gas car there’s far more benzene around you than in sunscreen. | | |
| ▲ | dylan604 3 days ago | parent [-] | | Okay, and? If you can’t see a difference in benzene as a byproduct vs an ingredient people lather in their skin and rub in sold as a way to protect against skin cancer while giving you chances of a different cancer as something totally different, then your being deliberately obtuse and not contributing to this conversation in any meaningful way. | | |
| ▲ | dzhiurgis 3 days ago | parent [-] | | My point is benzene is all around you. You willingly breathe it vs accidental trace amounts in a vital product. |
|
| |
| ▲ | Qem 3 days ago | parent | prev [-] | | IIRC Robocop predicted this. |
|
| |
| ▲ | Nursie 4 days ago | parent | prev [-] | | I mean, that’s a whole separate question really. Alongside which constituents may be long-lasting and harmful to (for example) marine life. |
|
