4 ms·

Wait, Walter, what is this "wait 20 mins before it becomes effective"? Did I miss something? Aren't the standard ingredients simply opaque to UV frequencies rig

by SiVal 6y ago

Wait, Walter, what is this "wait 20 mins before it becomes effective"? Did I miss something? Aren't the standard ingredients simply opaque to UV frequencies right out of the bottle/tube?

caw 6y ago
The standard Coppertone sunscreen says Directions: Apply liberally 15 minutes before sun exposure. Reapply: after 80 minutes of swimming or sweating; immediately after towel drying; at least every 2 hours I’ve always heard this as time to absorb to become waterproof, but I’m not sure if it’s actual skin absorption or the liquid used to convey the sun blocking compounds to dry or evaporate. Either way, apply and then wait.
- SiVal 6y ago
  I always (mis?)interpreted that as a way to get you to finish putting it on before you went into the sun, so you wouldn't get burned while possibly putting it on (a group of kids, for ex) too slowly while standing in the mid-day sun.
- buran77 6y ago
  When you film it in UV, sunscreen appears completely black from the first drop out of the bottle, meaning it absorbed all UV. The 15 minutes might be for applying or getting absorbed before there's a chance to get wiped off. This is a good video to highlight this [0], the sunscreen part is in the second half. Probably many more like it. [0] https://www.youtube.com/watch?v=o9BqrSAHbTc https://www.youtube.com/watch?v=o9BqrSAHbTc
- anonAndOn 6y ago
  I think the 15 mins is to allow sufficient time to dry so that you don't immediately sweat it off and/or wash if off in the pool/lake/ocean. It's got to stay on your skin to be effective.
vinay427 6y ago
There are chemical and physical active ingredients used in sunscreens, with many sunscreens containing a little of each. The physical components tend to work immediately as they block UV frequencies as you mentioned. The chemical components apparently need to be absorbed into the skin. This is a fairly succinct overview: https://blog.reneerouleau.com/chemical-vs-physical-sunscreens-pros-cons/ https://blog.reneerouleau.com/chemical-vs-physical-sunscreen...
- refurb 6y ago
  As a chemist I squinted at “need to be absorbed to be effective”. The molecules in sunscreen either block or absorb UV. Nothing gets “absorbed into” the skin. It just sits on top (the skin is an amazing barrier). The fact the molecule can absorb UV doesn’t change if it’s sitting in a tube or on top of your skin.
  - vinay427 6y ago
    Every source I could find indicates this distinction as well as the fact that chemical active ingredients need a bit of time to be absorbed, unlike physical ingredients. Maybe you could provide an explanation for how your claim seems to fit for chemical sunscreen active ingredients? Here's another excerpt from a different source: > Chemical sunscreens use up to a dozen ingredients that, when applied, are absorbed in the top layer of skin. They react with the skin to absorb UV rays and convert them into energy before they can harm the skin. > Chemical sunscreens aren’t as thick as physical sunscreens, so they are often used in sunscreens specifically made for the face as well as those found in spray bottles. Since chemical sunscreens need to be absorbed into the skin, they must be applied at least 20 to 30 minutes before heading outdoors. > Physical sunscreens, sometimes called “natural” sunscreens, include two ingredients: zinc oxide and titanium dioxide. Together, these ingredients sit on top of the skin and deflect or reflect the sun’s rays. Think of physical sunscreens like a shield, while chemical sunscreens are absorbed into the skin. Both ingredients work well to protect from UVA and UVB (broad spectrum) rays. Since physical sunscreens are thicker, they can leave a white cast on the skin. https://www.pennmedicine.org/cancer/about/focus-on-cancer/2013/july/chemical-sunscreen-vs-physical-sunscreen--whats-the-difference https://www.pennmedicine.org/cancer/about/focus-on-cancer/20...

by SiVal 6y ago

Wait, Walter, what is this "wait 20 mins before it becomes effective"? Did I miss something? Aren't the standard ingredients simply opaque to UV frequencies right out of the bottle/tube?

caw 6y ago

The standard Coppertone sunscreen says Directions: Apply liberally 15 minutes before sun exposure. Reapply: after 80 minutes of swimming or sweating; immediately after towel drying; at least every 2 hours I’ve always heard this as time to absorb to become waterproof, but I’m not sure if it’s actual skin absorption or the liquid used to convey the sun blocking compounds to dry or evaporate. Either way, apply and then wait.

SiVal 6y ago
I always (mis?)interpreted that as a way to get you to finish putting it on before you went into the sun, so you wouldn't get burned while possibly putting it on (a group of kids, for ex) too slowly while standing in the mid-day sun.
buran77 6y ago
When you film it in UV, sunscreen appears completely black from the first drop out of the bottle, meaning it absorbed all UV. The 15 minutes might be for applying or getting absorbed before there's a chance to get wiped off. This is a good video to highlight this [0], the sunscreen part is in the second half. Probably many more like it. [0] https://www.youtube.com/watch?v=o9BqrSAHbTc https://www.youtube.com/watch?v=o9BqrSAHbTc
anonAndOn 6y ago
I think the 15 mins is to allow sufficient time to dry so that you don't immediately sweat it off and/or wash if off in the pool/lake/ocean. It's got to stay on your skin to be effective.

vinay427 6y ago

There are chemical and physical active ingredients used in sunscreens, with many sunscreens containing a little of each. The physical components tend to work immediately as they block UV frequencies as you mentioned. The chemical components apparently need to be absorbed into the skin. This is a fairly succinct overview: https://blog.reneerouleau.com/chemical-vs-physical-sunscreens-pros-cons/ https://blog.reneerouleau.com/chemical-vs-physical-sunscreen...

refurb 6y ago
As a chemist I squinted at “need to be absorbed to be effective”. The molecules in sunscreen either block or absorb UV. Nothing gets “absorbed into” the skin. It just sits on top (the skin is an amazing barrier). The fact the molecule can absorb UV doesn’t change if it’s sitting in a tube or on top of your skin.
- vinay427 6y ago
  Every source I could find indicates this distinction as well as the fact that chemical active ingredients need a bit of time to be absorbed, unlike physical ingredients. Maybe you could provide an explanation for how your claim seems to fit for chemical sunscreen active ingredients? Here's another excerpt from a different source: > Chemical sunscreens use up to a dozen ingredients that, when applied, are absorbed in the top layer of skin. They react with the skin to absorb UV rays and convert them into energy before they can harm the skin. > Chemical sunscreens aren’t as thick as physical sunscreens, so they are often used in sunscreens specifically made for the face as well as those found in spray bottles. Since chemical sunscreens need to be absorbed into the skin, they must be applied at least 20 to 30 minutes before heading outdoors. > Physical sunscreens, sometimes called “natural” sunscreens, include two ingredients: zinc oxide and titanium dioxide. Together, these ingredients sit on top of the skin and deflect or reflect the sun’s rays. Think of physical sunscreens like a shield, while chemical sunscreens are absorbed into the skin. Both ingredients work well to protect from UVA and UVB (broad spectrum) rays. Since physical sunscreens are thicker, they can leave a white cast on the skin. https://www.pennmedicine.org/cancer/about/focus-on-cancer/2013/july/chemical-sunscreen-vs-physical-sunscreen--whats-the-difference https://www.pennmedicine.org/cancer/about/focus-on-cancer/20...