now this is a subject I have professional experience in, so I can provide a little more insight than usual (and I still have a photochemistry textbook from my 3rd year, I found it a fascinating subject) as other commenters have noted, most chemical filters work by internal conversion, and dissipate the excited-state energy through vibrational coupling with the ground state; they form relatively stable, long-lived and unreactive radicals, so they have plenty of time to do so this is why benzophenones, cinnamates and salicylates are a common structural motif in older filters - they're known to form relatively stable radicals (on the same subject, the mechanism for oxybenzone at 10:02 looks unlikely, given that benzophenone derivatives usually react with light at the C=O group between the rings) zinc oxide and titanium dioxide have a very high refractive index, so they scatter incoming UV light very efficiently; in more recent times, a number of manufacturers have started selling dispersions of these materials with a particle size around 50 nm, which both increases the efficiency due to Rayleigh scattering, and reduces any unpleasant white residue [EDITED TO ADD: sunscreen grade titanium dioxide and zinc oxide are always coated in water-insoluble substances to prevent them from reacting with other materials, and in the case of zinc oxide, to reduce its aquatic toxicity - in its untreated form, it's very poisonous to water-based life] the reason there's a much wider selection of sunscreens outside the US is because the FDA are very overstretched, particularly in regulatory terms, and so the wheels turn very slowly as an example: avobenzone, the first UVA-specific filter, was invented around 1973, became permitted for use in Europe in 1978, and eventually approved by the FDA in 1988 (incidentally, at 4:04 you got UVA and UVB the wrong way round; UVA filters were invented relatively recently because the effects of UVA weren't known) part of the reason is also because in the US, sunscreens are classified as medicines, and are regulated as such, whereas elsewhere they are classified as cosmetics on the subject of avobenzone, it's tricky stuff to work with, as it's only soluble in highly polar oils (e.g. C12-15 alkyl benzoate), has a tendency to self-destruct over time in UV light, and it knackers cinnamates as well; octocrylene is typically used to keep the reactions to a minimum more modern UVA/broad spectrum filters based on 1,3,5-triazines were pioneered by Ciba - now part of BASF - in the early 1990s, and were under patent for many years; most of them are generically available these days, but none are permitted in the US, again due to the general slowness of the FDA, which is a shame because they are much more benign than the more old-fashioned ones, having been subjected to very rigorous toxicological testing one of these (BEMT / Tinosorb M) takes the form of an insoluble dispersion, so it's not just a chemical filter but a physical filter as well, giving the best of both worlds hope this novel-sized tract is suitably informative!
"..filters work by internal conversion and dissipate the excited-state energy through vibrational coupling with the ground state.." after many years of thorough study in all kinds of fields such as quantum and chemistry i still wish to god to be able of truly understanding what this sentence means it'll be a dream come true
@@waelfadlallah8939 it was the most concise way I could summarise it, without going into an equally long tract about things like the Franck-Condon principle, vibrational relaxation and surface crossings as I said, photochemistry is a complicated but fascinating subject
@@lefthandedspanner you made me enthusiastic about getting a deeper dive into this extraordinary subject. If you have any recommendation about how to start or any useful reference it will be appreciated
@@waelfadlallah8939 for photochemistry, I can recommend "Modern Molecular Photochemistry" by Nicholas J. Turro as a good introductory text for sunscreens, I don't know of any textbooks that cover them in detail - most of my knowledge has come from industry
I love sunscreen. whenever I get the chance I like to drink a whole bottle between shifts at work to re-energise myself after a long day! Zinc is my favourite but SPF 40 does the job too although tastes a little ratty in larger doses
Fun fact: Hair removal lasers work by harnessing the melanin in your hairs and turning that power against itself. Normally, hairs have large amounts of melanin to help with absorbing UV so it gets picked up by the hair and doesn’t make it to the skin. However, if you have a laser specifically tuned to the exact wavelength that melanin absorbs, you can provide such a strong and focused blast of UV energy that the melanin absorbs it all and in the process generates a brief burst of thermal energy which fries the hair follicle all the way down to the root, killing hair production in that area. However, one rather unfortunate side effect of this is that for people with darker complexions, their skin contains almost as much melanin as their hairs and so people of color often have a much higher chance of getting burned during laser hair removal, since their skin is absorbing a lot of the UV and heat as well. For laser hair removal to work best, you need a high level of contrast between melanin levels in the hair vs melanin in the skin.
Lol I'm legit doing a presentation for my ochem class on organic sunscreens. I'd been having some difficulty finding a good explanation of how the active ingredients go about dealing with the absorbed UV. Thanks for pointing me in the right direction!
"Oh no we've produced too much thymine dimers, we now must commit apoptosis." is a gold scientific sentence. Now instead of saying "commit seppuku" I'll say "commit apoptosis". Thanks, That Chemist !
I really like this kind of content where you explain a topic through a chemical view. I think it was enjoyable to watch and hope for more in the future.
In some of your past videos you mention how a medicinal chemist will use different techniques/compounds for a certain synthesis and I was just wondering if you could make a video on the differences between the strategies they use/why they use different reagents
as an industrial chemist working in this field, I can say it's a combination of how effective the filter is, achieving a broad UVA/UVB spectrum of protection, how it feels on the skin, and the regulations in the region of the world where you intend to sell it outside the US, my workhorse sunscreen of choice is bemotrizinol / Tinosorb S, as it's stable, provides broad spectrum protection, is sensorially inoffensive and can easily be used in water-based or anhydrous formulas
you should really check out Labmuffin Beauty's videos and blog posts about coral reef bleaching and sunscreen toxicity! She makes a lot of content related to fearmongering about chemicals in personal care
One thing to note about SPF is that it significantly affects the _duration_ of effective protection. If half-life of sunscreen is 1 hour then in 2 hours your SPF30 will become SPF7, which is not really a good protection. While SPF100 will still be at around SPF25.
another question I have is: is the half-life even a useful concept for sunscreens? I was under the impression that it was mostly sweat and mechanical action that washed it off, making it ineffective, rather than like the chemicals inside it being used up. in that case it doesn’t seem like an exponential model would match the reality very well particularly once you get towards the end of the sunscreen’s effective period. this is mostly speculation on my part; I am not an expert and may be misremembering things I read ages ago. please correct me if I am wrong; I would love to learn more.
Great video. I'm very sensitive to sunlight, so this was quite interresting. I think theres a little mistake at 4:05 because you said UVC has en even higher wavelength but it's actually lower (It's the frequency that is higher) As far is I remember UVC sits around 200nm to 280nm, UVB is 280-315 and UVA 315nm - 400nm
Love this, I am a skincare obsessed lady and I wear sunscreen daily to protect from cellular damage. i'm very pale and don't hVe much natural protection! I like to know how the stuff I put on my face works
this video was really informative. As a biochemistry student as soon as you said thymine dimers you reminded me of my exam next 2 weeks. We also talk about DNA and what can damage it etc. And now knowing that my cells actually have to kill themselves after a sunburn I will be extra careful now ;)
Well, looking at beach pictures in the early 1900's people had shirts on, and that is what I prefer to protect my skin. A couple decades ago I read in a medical journal that the area of the skin in women that the most deadly melanomas develop is the scapular area of the back. This makes sense not only because of women summer fashion, but also because people naturally put their backs to the sun.
While it's true that oxybenzone and octinoxate can cause coral bleaching it's not clear to me that it's actually causing it in the actual environment since the concentrations used in those experiments were much higher then anything seen in the actual environment (they were doing experiments on corals in salt water tanks). So the jury is still out on whether it plays a role in coral bleaching out in the actual environment (although the biggest cause of bleaching in the environment is still thought to be global warming regardless). That being said the state of Hawaii still banned them just to be safe.
Another way to look at SPF is that with with SPF 30 you'll get the same amount of UV in 30 minutes with it, as 1 minute without. E.g. if you know you won't burn in 10 minutes without sunscreen, you'll probably not burn in 300 minutes (5h) with SPF 30. With perfect coverage and reapplication of course.
Excellent video! Although I think you made a mistake at 4:20 It's UVB that causes damage to the epidermis while UVA (not UVB) penetrates deeper causing wrinkles (I think both can cause cancer). At least this is what the FDA website told me.
Would’ve liked to have more time allotted to discussing the anorganic salts that are often used as nano formulations. There’s been quite the discussion on possible side effects among pharmacists during one of my further educational seminars after university.
Yeah nanoparticles have controversies but I don’t have firm opinions on them, and I try to do my best to only take authoritative positions which I can back up with my expertise and try to come to a conclusion on
That's a hot discussion in pretty much all branches of nanochem. The danger is that at the nano-scale they might be small enough to be absorbed by your body and enter cells and/or the bloodstream. That means there's no easy way to predict what will happen toxicologically anymore, because now the effect of particle size becomes a big unknown variable. It's entirely possible for a certain material to bio-accumulate at 100nm particle size, while being perfectly safe as both single particles and bulk material. The field of nanochem is still relatively young, so studies on long-term side effects of nanoparticles of any material are only just beginning. It will be a few decades before the fog will start to lift on that one.
I'm here again to remind about the beautiful compound dibenzylideneacetone. It is used in sunscreen, and it generates i think butane isomers when in contact with UV
I get sunburns very easy. My minimum is SPF 70, but I get 100, or 110 if I can. It's kinda difficult to find the really high SPF stuff, but from experience, that little extra protection really does make a difference, especially on shoulders, ears, and the back of the neck which are almost always directly in the sun.
This is so interesting. I always thought that UVA is what penetrated deeply to destroy collagen and UVB was more superficial but it's actually the other way around?
You are right, he made a mistake on that slide. Also worth noting is that SPF only deals with UVB because it causes sunburn. UVA penetrates deeper and can cause damage to DNA. This is why you need broad spectrum sunscreen,
I wonder if Thatchemist realises how hilarious these videos are purely from his delivery of the content. Someone who obviously has such a deep knowledge of what they're talking about explaining things in such a casual manner to laypeople like myself just makes me laugh all the time. Great Stuff.
These SPF numbers are so odd to me as an engineer. I think in ratios expressed in dB, so SPF of 100 means it’s a 20 dB reduction in UV exposure. SPF 50 is 17 dB, 30 is barely 15 dB. The difference between 15 and 17 would be likely negligible, especially since so much of it depends on human factor variables like consistency of application and thickness of the layer.
This came out while I was on “vacation” visiting family in the Midwest. Don’t know how I missed it, I even participated in the survey… either way, one of the bests yet. 11/10 bleached coral.
I just moved to Australia, so this is super interesting to me. Just a comment about your audio: There's a lot of mouth sounds. You may have your microphone a bit too close to your mouth (Edit: Or you may be a bit dehydrated. Have some water before recording). It's a bit distracting when using headphones to hear all the mouth sounds (we call it "smatter" in Norwegian). Just thought I'd mention it.
I’m working on it - the new videos should have fewer of them, because I spend time editing now, where lots of my earlier ones (like this video) were all recorded in one take with no editing
I really like this video - explaining something that I'm familiar with. (I sunburn in minutes - I'm just a very pale white person.) Are you planning to do anything related to food or cooking? I'm a big fan of the Maillard reactions - making my food an appetizing brown and giving it a nicely toasted flavor. I'm also "academically" interested in pharmaceuticals....
Never did understand why they didn't just add more fluorescent chemicals. Guess people don't want to look weird colors under UV unless they're at a rave? Wonder about the effectiveness of fluorescent body paint compared to traditional sunblockers. . . (And I wonder about the possibility of ruby powder, given how effective it is at blocking UVA and B, and downshifting it to nice ruby red light. Abrasive AF however. . . but it is Al2O3 mixed with some Cr2O3 IIRC. Someone correct me if I'm wrong on the chromium oxide)
The takeaway is not that you should wear sunscreen. The takeaway is that a person who wants to minimize their UV exposure will achieve that goal a lot better by wearing sunscreen of any type than by not wearing any. A vitamin D deficient person with dark skin who is unwilling or unable to take supplements should avoid any sunscreen without discrimination because any sunscreen will prevent them getting UV exposure about as well as any other.
a completely new kind of sunscreen that lasts more than a month could be based on a thing like transparent Henna. A chemical at henna does a Michael reaction with the keratin protein of skin and links a colored molecule to it durably, not washing off. There are molecules that do the Michael reaction that are transparent. Linking that michael reaction group to a UV absorber then makes a sunscreen that lasts longer than a month. This could be a completely new anti-photoaging product as a new revenue product. Notably, the UV absorbers in commercial sunscreens last only a few hours, but, fortunately, the UV absorbers in printing inks lasts months. Those chemicls could be tested to find out which are body harmless, and be a part of the michael reaction sunscreen that lasts longer than a month. This is a complimentary public domain idea and can be commercially developed without further contact 7/29/23 Treon Verdery, North Bend, Oregon
The bottle of 50+ sunscreen I have contains 6 UV absorbers: octocrylene Homosalate butyl methoxybenzyl methane Octyl salicylate Bemotrizinol Ensulizole The list should be by amount container, right? Only water comes before active UV absorbers in this stuff.
that's right, assuming of course that the manufacturer/brander is following the relevant regulations if it's made in China it could contain damn near anything
The only good thing about the sunscreen regulation situation in Australia is that the quantity of active ingredients in the formulation must be stated in mg/g - other than that one thing, everything else concerning regulation sucks i.e. there is minimal to no adequate regulation.
@That Chemist how can we correlate the properties of a material on whether it reflects, absorbs or is transparent with different wavelengths of light with its structure and other chemical properties.
IIRC, old school mechanics used to wash their hands in benzene/gasoline as it gets rid of grease easily. Imagine that: not only being surrounded by fuels and oils all day but also exposing yourself to carcinogenic chemicals to wash your hands.
Huh I was just at a barbecue yesterday and I decided to take a look at the ingredients in the sunscreen I put on. I suppose it's not too big of a coincidence considering yesterday was July 4th but even so this is funny.
isn't a singlet oxygen technically peroxide? or is it just an analogy in this case? Really glad I was recommended your channel recently, very informative.
No, both types of oxygen are O=O, peroxides are O-O (double vs single bond). The difference between normal vs singlet oxygen is in the electron configuration. In normal oxygen the 2 highest-energy electrons have the same electron-spin. In singlet oxygen these electrons have opposite spin, which is much less stable, and the oxygen is therefore much more reactive. For most compounds these less stable electron configurations will revert back to the most-stable (ground state) configuration almost instantly, but singlet oxygen cannot do that due to weird quantum mechanics (selection rules, the transition is both spin- and parity-forbidden). So singlet oxygen is "trapped" into existing long enough to do all sorts of chemistry.
One thing I think you missed mentioning is that last time I checked anyways, there was no clear evidence that sunscreens of SPF >70 are any better in practice than SPF 70. So it's not worth shelling out for SPF 100 or whatever
If I remember correctly, at some point recently (but maybe no longer?) Canada capped the labelling of SPF values to something like 45, so anything “stronger” than that had to be called 45+. I believe it’s for the reason you mentioned. (This may no longer be the case; I can’t find information about it and a web search reveals that walmart·ca is selling SPF 70.)
SPF 100 actually is no more expensive than SPF of any other value. In most cases, the actual chemicals used in the product are only a few cents worth. The big bucks products simply give the merchants more profit.
@@jasonnikakis6033 There is no need to be that sassy. Most sources say that you still get tanned with sunscreen, duh, but I couldn't find information on the tanning rate.
There's basically no amount of sun exposure that's "safe", people used to think that you could do short sessions in sunbeds to build up a tan and have less risk of sun damage, but that just puts you at more risk of permanent damage.
I noticed that octacrylene has a nitrile group on it - which brings the question I have - Why are some compounds that have a nitrile group not that toxic when there's basically a cyanide group hanging out?
Now this is an interesting question, because after oxybenzone, octocrylene is next on the list to be wary of. Normally Octocrylene is used in formulations at about 2-3 times the concentration of Avobenzone. This has been happening for a decade now since it was found that Avobenzone is decomposed rather rapidly by UV, and the protection of your sunscreen degraded rapidly. !! Octocrylene in excess protects the Avobenzone via a funky photochemical interaction (triplet-triplet quenching) and retards the rate of decomposition by over an order of magnitude, long enough for the sunscreen to remain effective for the recommended re-application rate.
I never got an answer on this, but can you tell if people who are not outside, or very briefly, that their sunscreen application is still good after several hours since sun light hasn't reacted with the chemicals on the skin? In other words, how often should one reapply if they just applied once for a 15 minutes sun exposure before they come back inside. Assume no windows and office fluorescent lights and computer screens.
@@That_Chemist well. I do apply quite a bit. So much so that I'm worried that I'm wasting it. With the costs rising and all, I'm hoping to retain value out of my value brand sunscreens.
Always wondered why the aromatic character of benzene/pah's blocks UV so well and nothing else really can?? The electron shell absorbs the high energy photons?
electrons are excited to higher energy levels, and they slowly release energy in the form of heat (depending on allowable transitions - quantum chemistry stuff)
So this might not make sense, but is there any kind of chemical that can absorb visible light or UV photons and translate that energy into conformation changes instead of actual bond changes? I tried to figure this out a while ago but as far as I could get was some cyclohexane derivatives having conformer energy differences on the order of a fraction of an eV.
@@That_Chemist Huh. So it looks like the cis-retinal is both the one that is the higher energy conformer and the one that changes conformation when struck with a photon (into trans-retinal). It has to be enzymatically reset, consuming ATP. So kind of like a mousetrap being sprung by a photon. Thanks for knowing a molecule off the top of your head that would do that but I was really hoping for something that could store the photon's energy and potentially release it via a change in conformation, especially something that exhibited fluorescence or phosphorescence but through conformational changes. More like a mousetrap being set by a photon rather than sprung. There's a lot of weirdness that could be done, like a laser that runs on conformation changes or potentially solubility changes of a chemical across a polar/nonpolar interface mediated by exposure to visible light. Anyway, I have a lot more stuff to read for now I guess. Piperidine has two different chair conformers which are preferential in polar vs nonpolar solvents but there's very little actual energy difference between them.
it'd be very inefficient, the refractive index would be too low zinc oxide and titanium dioxide were originally used for white paint (and still are) due to their very high refractive index
@@00bean00 I've had poison ivy rash. Covered in Calomel lotion - that's Zinc Sulfide. DimethylSulfone is sold for animal and human arthritis and found in foods, doesn't stink, and low toxicity. I didn't think dithiobenzil was worse smelling than my roommate's farts.
Your conclusion doesn't follow. Depending on the strength of the sunlight, your skin, and how long you're in the sun, it may be impossible to get a sunburn. In which case, there's no reason to use sunscreen. Not to mention, clothing or shade.
The ideal process for a sunscreen molecule is to absorb the photon and do internal conversion directly from the singlet excited state. If it also does so from the triplet excited state that's good also. Those processes leave behind only the heat of the internal conversion process. Now that I think of it, I wonder if you could also make a sunscreen based on photoisomerization, which is in some cases a very fast process, sometimes
Be careful when dealing with ratios. you are claiming their isn't much difference between 30 an 50 at one percent which isn't much if you are looking at the amount of light absorbed but from the perspective of the skin factor 30 is 1.5 time more UV that factor 50 which is a huge difference.
@@That_Chemist yeah but the negligible needs to be justified based on impact. Using the same reasoning I could say the CO2 concentration has gone up 0.15% from 0.25% to 0.4% which is negligible, or Its relative concentration has gone up by 60% which isn't negligible. If reducing to 3% reduces the rate of sunburns to say 1 in 10 to 1 in a 1000, then maybe you have a case, but without that piece of information clamming a reduction by about 30% as negligible need to be justified. Sorry I'm picky on these but this is one of the easiest and most common way of misleading people.
@@MrTheboffin it's only a 30% reduction by comparison to an already good level of reduction. The assumption being made here is that the amount of UV hitting your skin is proportional to the level of damage (which is what matters). The way you're using statistics is actually the misleading one, which I would say arguably is the more prevalent mistake.
@@Zekei1234 "The assumption being made here is that the amount of UV hitting your skin is proportional to the level of damage (which is what matters)." so we assume that an increase by 30% damage is negligible ? That is only true if the initial damage in it self is negligible which hasn't been demonstrated. Factor 30 might be enough for some people, it probably more than enough for me because I tan very easily. For someone who factor 30 is not enough 30% difference is enormous.
