Benzene in your products, Part 1: Bad science

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How to cite: Wong M. Benzene in your products, Part 1: Bad science. Lab Muffin Beauty Science. April 16, 2024. Accessed May 17, 2024.

It’s now Round 5 of “benzene in your products is giving you cancer” – over the last three years, this “known human carcinogen” been found in hand sanitiser, sunscreen, deodorant, dry shampoo, and now benzoyl peroxide acne products. 

I previously talked about benzene in sunscreen and dry shampoo, but it’s time for a deeper dive into these findings, and the lab behind them, Valisure. There are a lot of flavours of wild here, so I’ll be mostly sticking to just the scientific aspects, but I’ve come across some interesting less-sciencey articles about them too.

In this part I’ll be factchecking what Valisure are saying about benzoyl peroxide, and benzene. In part 2, I’ll be talking about red flags about Valisure in general, and go through some possible explanations for all of these issues.

This is adapted from my video, which I think is some of my best work, and probably presents things a bit better than this post! 

valisure benzene video

Inflated temperatures for benzoyl peroxide experiments

Valisure tend to frame their results in pretty misleading ways, and the latest benzoyl peroxide announcement is a prime example. Here’s what happened, Valisure’s version:


Benzene, a Known Human Carcinogen, Can Form at Unacceptably High Levels In Both Prescription and Over-the-Counter Benzoyl Peroxide Products

This sounds really scary, and (in my opinion) it’s meant to, for reasons we will discuss. And it worked.

Lots of posts, lots of panic – just based on what Valisure said (and sometimes, without even reading Valisure’s report):

tiktoks fearmongering about benzoyl peroxide

I’ve talked about peer review and how much slips through – there’s been more examples lately, and it also looks like people are using ChatGPT to do the peer reviewing. So we need to be more careful with something that hasn’t even gone through that.

don't trust someone just because they used "save to pdf" poster

First, we need to add a disclaimer:

…benzoyl peroxide products form benzene if stored at unrealistically high temperatures

In Valisure’s petition, the results start by mentioning that they tested products they bought (assuming room temperature = 25 °C or 77 °F), then kept them at 37/40, 50 and 70 °C (98.6/104, 122 and 158 °F) and tested them.

But for mysterious reasons (foreshadowing), they don’t tell us specific numbers for the lower, more normal temperatures… which is weird, because their previous benzene petitions had huge tables of them:

tables of benzene-contaminated products from valisure petitions

Instead, they give us lots of pretty graphs for 50 and 70 °C, and one product they tested at 40 °C:

valisure petition graphs

This is a huge red flag to me, as a chemist. Heat makes reactions happen faster, like benzoyl peroxide breakdown, so there’ll be more of a benzene buildup. It’s like using up a perfume with one spray a day, versus using it all up in a few hours – at a slower rate, the level stays acceptable as the perfume molecules have a chance to drift off over time. 

Valisure say these temperatures are “reasonable”, and they have citations for this. So let’s use One Weird Trick for Spotting Dodgy Science, Doctors Hate Her: actually read the citations!

Is 50 °C a “reasonable temperature”?

For 50 °C, it’s a reasonable temperature “during distribution and handling by consumers” – Valisure cite a page from the FDA website. But if you track down what the FDA are talking about (their reply to a petition from Emery Pharma, posted on the same day), they specify 40 °C:

FDA Emery Pharma petition reply

50 °C is also supposedly “an accepted incubation temperature for accelerated stability studies”, where products are heated to approximate what happens normally, in a shorter time. For example, 6 months at 40 °C roughly approximates what should happen in 2 years at room temperature (25 °C).

Valisure cite a paper from a journal whose home page… doesn’t exactly inspire great confidence:

ijapb homepage
Some of the text scrolls from right to left – you can actually hover over them and try to get them to line up.

The paper mentions 50 °C once, at the end, with no reference. So you have to ask: why did Valisure decide to cite this random paper, instead of the official WHO and ICH international standards that this paper mentions, and even provides in a nice table?

Is it because… the standard accelerated testing temperature is 40 °C?

Ghimire stability testing temperatures

(Also if this doesn’t say something about the state of peer review – Valisure’s Environmental Health Perspectives paper also cites this article. I actually think ChatGPT could’ve improved the peer review here…)

50 °C is usually used for stress testing, which is different from accelerated testing, as seen in the official FDA guidelines (the FDA who they’re supposedly writing this petition to, who they could totally have cited instead). You’re meant to get false positives in stress testing – for example, if the product separates, you’d check that it’s actually likely to happen at normal temperatures before trying to fix it. But perhaps “stress” doesn’t really match the whole “reasonable temperature” vibe they’re going for.

Interestingly, at the start of the petition, Valisure cite a paper that cites another paper with rate constants, which we can use to calculate how quickly benzoyl peroxide breaks down. And – interestingly – you can see the temperature at which benzoyl peroxide would be predicted to break down completely in their testing time of 18 days: 

benzoyl peroxide rate constants

It’s 50 °C. Maybe it’s a coincidence?

Is 70 °C a “reasonable temperature”? 

After heating the products at 50 °C for 18 days, Valisure took the products with the lowest benzene, and… heated them up even more. This time it’s 70 °C or 158 °F for 14 to 18 days that’s a “reasonable temperature”.

Again, the citations don’t support this assertion. They again cite the FDA referring to 40 °C. They also claim it’s “within the reported temperature range of a hot car”. But if you search “hot car temperature”, almost all sources say 50-60 °C (130-140 °F). So Valisure cite another cherrypicked paper, where 70 °C is how hot a car CAN get (the maximum, not the average temperature recorded), if parked in the full sun and it’s over 34 °C (93.2 °F) outside.

So their experiment is essentially simulating the very “reasonable” conditions of a car being parked in the sun, and the sun not setting for 14 to 18 days, after these products had been sitting consistently at 50 °C – the hottest temperature ever recorded in Australia – for 18 days. Global warming is bad, but it’s not THAT bad (so far).

Valisure also claim that 70 °C can be used for accelerated testing, citing an online calculator to say 43 days at 70 °C is equivalent to 3 years at room temperature. However, too high a temperature can give invalid predictions in stability testing, as heat can cause different reactions to happen (this is explained on an FDA page they cited in a blog post – there seem to be quite a few examples of Valisure being unable to read their cited sources…).

For example, 13 minutes at 75 °C will give a perfect sous vide egg. According to the formula the calculator uses, this is equivalent to 33 hours in a 2.5 °C fridge, which most assuredly does not cook your eggs (I’ve tried).

Valisure’s own experiment seems to be trying to tell them this: the product packaging ruptured in a week at 70 °C, which would be 5 months normally, according to the calculator. Benzoyl peroxide generally doesn’t hulk out of its container at 5 months.

Is 40 °C a “reasonable temperature”? 

The petition includes one experiment at 40 °C for 17 hours, which I would say is actually a “reasonable temperature”. But again, their reasoning is bizarre: it’s “the approximate temperature a bathroom can reach during a hot shower”, and – surprise – it’s not what their citation says.

It actually shows that bathrooms get above 35 °C in summer, sometimes, for about 15 minutes:

bathroom temperatures aizawa

I’m guessing they read the graph wrong, and thought the lines for humidity (blue, orange, light green) were temperature (navy, red, dark green). Or maybe this was the best reference they could find to justify their arguments, and they were hoping we would all read the graph wrong. (I’m not sure which is more likely at this point.)

Temperatures during transport?

A side note – some people have said the products could get this hot in trucks and warehouses before they get to the store. But even Valisure don’t claim this.

Benzoyl peroxide is an over the counter drug in lots of places, including the US, so by law (e.g. cGMP in the US, Good Distribution Practice in many regions), the temperature is controlled until it gets to the pharmacy. This is designed so it’s really hard to screw up – for example, temperature sensors are used to monitor shipments. If this was a big problem, most sunscreens just wouldn’t work. If you’re getting your products delivered to your home, don’t buy it in the middle of summer, just like for sunscreen.

What’s going on?

This is a very high level of citation abuse for a petition with two science PhDs as authors, who should know how to read these studies. In my opinion, the best explanation is that Valisure are using artificially high temperatures to get more dramatic results, and they’re trying to convince us they didn’t.

What are the benzene levels at room temperature?

A few days after the petition, and a lot of people (including me) had roasted their temperature choices, Valisure posted an article that doubled down, but also gave more info:

Of the 66 benzoyl peroxide products tested, 10 products had over 10 ppm of benzene and 19 products had over 2 ppm

They point out the first data point in each 50 °C graph is before heating, which a lot of us had already worked out. The highest benzene levels measured seem to be around 20 ppm – IF we assume nothing weird happened before they tested them, and IF they measured the benzene levels correctly (foreshadowing).

Some of these levels are higher than 2 ppm, a common limit for benzene in oral medications (ICH and USP), which isn’t great. But official safety limits are generally pretty precautionary – how scary are these numbers, actually?

Cancer shenanigans

According to Valisure, very scary. (To no one’s surprise.)

Benzene isn’t good for you, and I think it’s great that regulations are reducing our exposure. This is exactly the sort of thing I think government regulations should be targeting. But the commentary makes it sound like – well, what all the TikToks are saying:

"We are rubbing cancer into our skin"
“We are rubbing cancer into our skiiiin”

What Valisure say is technically true, but it’s presented in a way that ends up being misleading, because most people reading their press release and petition don’t know much about benzene.

It’s basically this logic:

Mashelle Wrong: “If you have this, throw it out – it has sodium chloride which is really dangerous. It’s been linked to high blood pressure, kidney disease and strokes.”


Everything my evil twin said about salt is technically correct, but it’s ridiculous when applied to tiny amounts in shampoo that you’re not drinking (presumably – I don’t know your life). Anything can sound scary if you strip away the context.

Here’s where Dr Christopher Bunick comes to the forefront. He’s a dermatologist who essentially acts as Valisure’s go-to toxicology spokesperson. They quote him a lot, he’s on their paper, and he’s the main person “educating” dermatologists about benzene. He’s an editor at Dermatology Times, a popular magazine for dermatologists.

He claims he has “no financial relationship with Valisure”, and if that’s true, I feel a bit sorry for him. Valisure are letting him say stuff for them that’s fairly cringey, if you know anything about benzene or toxicology.

But since other dermatologists also generally don’t know much about benzene or toxicology, many are just trusting and repeating what he says. It then spreads to journalists and influencers who assume dermatologists know everything about skincare products, including ingredients that aren’t usually in them.

There are two main phrases he repeats a lot in Valisure’s press releases, petitions and in media interviews:

“Benzene is a group 1 carcinogen, known human carcinogen, and it’s in the same category as asbestos, formaldehyde, and lead. So you wouldn’t let your children or any of your relatives play with asbestos or lead. You’re gonna let them play with benzene?” 

“any concentration of benzene greater than zero is not safe…there is probably no safe level of exposure to benzene”

(from his talk at the South Beach Symposium in 2022)

“Known human carcinogen” and “no safe level of benzene” together sound genuinely scary. But scientists don’t use these phrases in the way we’d interpret them normally.

Known human carcinogen

“Group 1” or “known human carcinogen” means the evidence of a link between the carcinogen and cancer is solid. It doesn’t mean that you’ll definitely get cancer if you’re exposed to any amount – the dose still matters.

He and/or Valisure have cherrypicked some of the scariest examples of Group 1 carcinogens (lead, asbestos, formaldehyde) to compare with benzene. Processed meat, sunlight, and wine are also “known human carcinogens”. They’re not great for you, but I don’t think he’s knocking salami or wine out of his relatives’ hands or locking them indoors. (Maybe he is? One weird trick, relatives hate him!)

No safe level

“No safe level” is also weird toxicology language – it means little bits will still add to the risk.

For example, if I tap a mug lightly enough that it doesn’t move, that’s a “safe level” that didn’t add to the risk of it falling off the table. But even drawing a teeny tiny dot with a pen is going to increase the risk of it running out of ink – there’s “no safe level” I can draw. But dose still matters – there’s a huge difference between a dot and colouring in a whole page.

(Note: The whole idea of some carcinogens having “no safe level” of exposure is actually a controversial concept to begin with, and is mostly used as a conservative, just-in-case approach in regulatory toxicology – it looks like there actually IS a “safe level” for benzene. But we’re rolling with it here to give Valisure as strong a case as possible. Thanks to Mo Skin Lab for this addition, as well as looking over some of the toxicology in this post and the video!)

And this sounds really scary with benzene, because we don’t have context. But alcoholic drinks and sunlight are also “known human carcinogens” with “no safe level of exposure”. Any of the UV photons going into your skin could be the one that triggers cancer.

But we don’t freak out when we get a tiny bit of sunlight, or drink a sip of wine – because we know those are more like a tiny dot. Not everyone who gets tiny exposures of these will get cancer from them.

So we need context – is the benzene from these products a dot or a page of ink?

Concentration shenanigans

Unsurprisingly, Valisure lean towards the latter. 

One thing that tends to be missing from Valisure’s provided context about benzene is that it’s everywhere. Benzene is in fossil fuels, and our whole civilisation has been running on fossil fuels for a really long time.

There’s about 1% or 10 000 ppm benzene in petrol (which is gasoline, if you use Fahrenheit). Obviously we don’t purposely put this on our skin (if you do, you should stop). But if you’ve ever accidentally touched some while filling up your car, the benzene level is about 500 times higher than the most contaminated benzoyl peroxide products at room temperature (20 ppm).

But the main concern is usually breathing benzene – it’s in the air everywhere. You’re breathing it right now.

Valisure did not bother telling us this when they started going on about how “there is not a safe level of benzene that can exist in any skin care product” – unless you’re keeping your products completely sealed forever, there’s benzene from the air in there.

And this brings me to THE most mindblowing part of this for me – and I can’t decide if it’s Valisure being really clever, or ridiculously incompetent…

Valisure use “parts per million” (ppm) and “parts per billion” (ppb) a lot to talk about how much benzene there is, and compare different situations. But there are a couple of issues:

Different units for ppm

These units are calculated differently when we’re talking about benzene in air, versus in everything else, like products (I’m going to call this “air” and “liquid” ppm – chemists, I know, don’t @ me).

ppm air vs liquid

It’s like degrees Celsius and degrees Fahrenheit, except scientists almost never say which ppm they’re using (we really need to get on that). Benzene is a relatively heavy molecule, so 1 ppm in the air (calculated per molecule) is equivalent to 2.7 ppm if we calculated it by mass, like we do for products.

Concentrations aren’t amounts

ppm and ppb are concentrations, which can’t be directly compared – they aren’t actual amounts. Eating a few grains of 100% salt (1,000,000 ppm) isn’t 100 times more salt than eating a bag of chips with 1% salt in it (10,000 ppm), just because you diluted your 11,500 grains of salt with potatoes.

It’s the amount of benzene – the dose – that’s important. To calculate the dose, we multiply the concentration by how much air we’re breathing, or benzoyl peroxide we’re using:

concentration = \frac{amount(benzene)}{amount(total\ sample)}

And the difference here is huge. We breathe about 15.5 cubic metres of air a day, which is about a quarter million of these tubes (60 mL). So to work out how much benzene we breathe in a day, we multiply the air ppm by almost 50 000. But to work out how much benzene is applied in a benzoyl peroxide cream, we divide the ppm by about 1.5.

And air ppm tells you how much is actually going into your lungs, but for products, skin doesn’t absorb benzene as well and you won’t breathe it all in – a lot of it is just going to float off.

All of this means that the same ppm ends up being a lot more than 75 000 times the difference in dose.

On top of this, being exposed to a whole bunch of benzene at once (like if you apply a product) is actually safer than the same amount over a longer time (like if you’re breathing it in air). The enzymes in your body that turn benzene into cancer-causing metabolites have a limited capacity – if they’re maxed out, less of it becomes carcinogenic.

benzene metabolic pathways

So we can’t directly compare ppm in air to ppm in a product.

Guess what Valisure do all the time? (in my opinion)

They’ll talk about the liquid ppm in products, and then the air ppm that causes health problems… without bothering to mention that these are not the damn same. The doses are thousands of times different.

benzoyl peroxide petition ppm

Here are some examples of Valisure and Bunick making far more direct comparisons…

Dr Christopher Bunick’s talk (“Update on Contamination in Skincare Products”) at the 20th Annual South Beach Symposium, February 2022:

“1.6 part per million [air ppm] is the threshold for starting to see leukemia risk increase..”

“…benzene in their products range from 11 to 24 parts per million [liquid ppm]. Does anyone remember the number I told you? The increased threshold 1.6 [air ppm]

David Light, Valisure’s former CEO and current president, “Contamination in Consumer Products: The Science and Its Impact”, September 28, 2021:

“this is data from the EPA, looking at benzene in the air… these levels are approximately 0.0003 parts per million of benzene or a third of one part per billion [air ppm]. And what Valisure is finding in hand sanitizers is over 50,000 times that limit and in sunscreens over 20,000 times that limit [liquid ppm].”

david light benzene concentrations

There are also some pretty unrealistic choices here, that make this look even scarier:

  • There’s usually 2-4 times less benzene outdoors than indoors (we spend most of our time indoors)
  • The numbers (50,000/20,000 times) are based on the absolute highest outlier measurements Valisure got.

But even if we just sort out the concentration/dose issue, these comparisons are thousands of times too high:

And it’s really interesting watching this slide evolve over time.

Here’s the version after their antiperspirant petition – it’s shown in liquid ppm:

david light benzene concentrations 2

Then here’s the dermatologist in 2022 – for dry shampoo, they’re actually using an experiment where they measured air ppm!

Bunick 2022 dry shampoo

It’s still not quite a fair comparison:

  • ”Short term” is the highest measurement, i.e. if you spray dry shampoo straight at your face and breathe it continuously
  • ”Long term” is if you spray your dry shampoo full blast for 10 seconds, and all the benzene stays trapped in the bathroom with you and breathe it “long term”
  • Both used a different measuring method (SIFT-MS) that gives 10-50 times higher readings

But just for these two, they fixed it! They actually fixed it!


But THEN, at the 2024 AAD meeting, he presented a new version, with benzoyl peroxide added… but they undid the thing they fixed – the dry shampoo number’s gone up by 100 times:

bunick 2024 aad slide

It’s good to do a reality check when you finish a calculation. Like, people have been using benzoyl peroxide for 60 years – are benzoyl peroxide users or people with acne 60,000 times more likely to have leukemia? And benzene generally messes up blood counts before you get blood cancers – Do a lot more people with acne have abnormal blood counts? Do women who use dry shampoo that’s meant to have half a million times more benzene than normal? Or are these wild comparisons?

And even if that didn’t cross their minds, shouldn’t they realise it’s weird that their new method that they said gives 10 to 50 times higher concentrations gave them a lower comparison? Wouldn’t it be responsible to think about these things at some point over the last 3 years?

This slide also shows why they probably glossed over the room temperature readings for benzoyl peroxide. All of the other numbers were calculated from the very highest measurement in each petition – for example, the number for dry shampoo was the highest single spray they measured, not even an average from that can.

So it looks like the absolute highest number for benzoyl peroxide was similar to antiperspirant: 17.7 ppm. And if we factor in how little benzoyl peroxide we use, this is the least dramatic product so far – it ends up being less than breathing outdoor air.

Comparisons by dose (corrected from concentration):

fingertips benzoyl peroxide
Two fingertips of benzoyl peroxide = 0.75 g

Someone at Valisure seems to know this is wrong. Because in the 2021 sunscreen petition, they multiply the concentration by the amount of product to get the dose:

“At the FDA conditional restriction limit of 2 ppm [concentration] for benzene, 28.5 g of sunscreen [product amount] would contain 57,000 ng of benzene [applied dose] in a single application which may reasonably be used 4 times per day, therefore amounting to 228,000 ng of benzene exposure per day.”

It’s certainly interesting that Valisure only remember to multiply by the product amount when it’s large (though half a cup of sunscreen every day is pretty unrealistic), but use diluting-with-potatoes logic the rest of the time. But in the petition, they follow with a wild comparison anyway, to the safe dose of a completely different substance, NDMA:

“the probable human carcinogen NDMA is restricted in drug products at concentrations similar to benzene, specifically 0.3 – 3.0 ppm in -sartan medication, and has a corresponding permissible daily intake of 96 ng. Using NDMA as a comparable benchmark, sunscreen products applied according to amounts consistent with FDA researchers’ studies and contaminated at 2 ppm benzene, will expose an individual to 2,375 times the acceptable daily limit [of NDMA]. In Valisure’s limited evaluation of sunscreen products in the United States and utilizing the aforementioned benchmark, the highest benzene detection of 6.26 ppm equates to approximately 695,800 ng of benzene in one day or 7,248 times the NDMA limit.”

There are quite a few examples where Valisure don’t seem to realise different things have different safe levels. Just because it’s safe to have 8 glasses of water doesn’t mean it’s safe to have 8 glasses of vodka. Two science PhDs signed this, plus their CEO, and everyone keeps mentioning how they went to Yale…

Yale, this is not a good look for you.

What’s the actual risk?

So what’s the risk from benzene in benzoyl peroxide, if we don’t assume we inhale a quarter million tubes of benzoyl peroxide a day?

This is a rough estimate (thanks to Dr Nini Munoz for the calculation and image) – given:

  • Highest benzene in the benzoyl peroxide products = 20 ppm
  • Two fingertips used per day = 0.75 g
  • Daily dose = 15 µg benzene
  • Applied every single day for a whole lifetime, from birth (you know how pimply newborns are) = 78 years 
  • Benzene is absorbed as well as if we inhaled all of it (again, a massive overestimate)

We’d have an increased cancer risk of about 8 in a million, which is 0.0008% on average, per person. By comparison, the lifetime risk of cancer is 1 in 2 for men (~50%), 1 in 3 for women (~33%).

benzene risk visualisation

  • Disclaimer: This type of occupational risk assessment offers only a basic estimate of real-life risk. Cancer typically arises from a complex interplay of multiple risk factors (age, lifestyle, carcinogen exposure, certain infections), sometimes even in individuals without apparent risks. Quantifying the exact contribution from each factor remains challenging. Standard risk assessments for carcinogens assume that risk increases as a function of cumulative dose. Inhalation Unit Risk values (used here) may not directly apply to dermal exposure, expected to be the primary risk from topical products. Benzene isn’t a concern dermally outside of occupational settings, so the associated risk should be minimal.

For comparison, here are some other sources of benzene:

  • Cooking on a gas stove: 100 µg benzene produced per meal (cooked with one burner on high, one on low and oven at 350 °F for 30 minutes – not all benzene inhaled)
  • Petrol station while refuelling: 9.4 to 306 µg (average 110 µg) inhaled in 5 minutes (assuming light intensity air exchange = 1.25 × 10-2 m3/min)
  • Inside a house (data from US, Canada and France): 31 to 63 µg inhaled per day

Valisure actually highlighted a similar lifetime risk calculation in their press release, but in their wording, it sounds like if you left benzoyl peroxide in your “hot car”, you’d have 1000 times the risk of cancer… which certainly sounds scary:

“Incubation of a Proactiv® product at the temperature of a hot car (70°C) resulted in the detection of benzene in a compact car’s volume of air at ~1,270 times the Environmental Protection Agency’s (“EPA”) calculated threshold for increased cancer risk by long-term inhalation exposure to benzene.”

But if we add in all of this extra context:

“Incubation of a Proactiv® product at the temperature of a hot car, left in full sun from 5 am to 9:45 pm at >34 °C/93 °F (70°C) resulted in the detection of benzene in a compact car’s volume of air at ~1,270 times the Environmental Protection Agency’s (“EPA”) calculated threshold for 0.0127% increased cancer risk by long-term inhalation exposure to benzene, if this level was inhaled continuously for 78 years.”

Or you can think about it this way: if 7900 people all got into cars parked like that with benzoyl peroxide in them, without airing out the car first, even a little bit, and they all kept breathing that level of benzene for 78 years… you’d expect ONE of the 7900 people to get cancer from the benzene.

To me, that seems pretty reassuring, and not really worth the melodramatic statements.

car benzene calculation risk

If you’re wondering – the biggest thing you can probably do to reduce benzene exposure is not park your car in a garage attached to your house. That comes from probably the top benzene toxicology expert, Professor Martyn Smith (via journalist Janna Mandell) – he’s the guy they keep quoting for “no safe level of benzene”, and here’s what he said about Valisure’s sunscreen petition:

“I don’t usually like downplaying public health risks, but I also don’t like scaring the public unnecessarily when there’s […] no need for that.”

What have other experts have said about Valisure? We’ll talk about that in Part 2…

Extra thoughts that didn’t really fit elsewhere

  • The Ghimire paper they cited is full of tortured phrases, which is usually a sign of plagiarism.
  • Valisure keep mentioning “online calculators” for predicting accelerated testing times, which is very bizarre because these calculators are a less precise version of the formula I used for the egg (their linked calculator rounds it off to the nearest day, but the site has the formula elsewhere). Why not… use the formula instead of citing a calculator? Do they not understand how calculators work?
  • In the petition, Valisure suggest that benzene contamination could explain the potential risk of skin cancer that was investigated for benzoyl peroxide in the past, due to animal studies. But it doesn’t. Not all cancers are the same – benzene is linked to blood cancers, and there’s no convincing link to skin cancers. Benzene was used as the base for lots of animal tests on other ingredients for skin tumours, and not all of them showed positive results. Benzene needs to be metabolised before becoming carcinogenic, and not much of this happens in the skin. The much, much more likely mechanism of cancer formation from benzoyl peroxide (which only seems to be a risk in specific animal models) is free radical formation, which is how UVA causes skin cancer.


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