Sunscreen safety and the FDA situation: Huberman’s skincare podcast response (Part 2)

The most controversial topic in Dr Andrew Huberman’s skincare episode is probably sunscreen safety, which is hugely misunderstood even by scientists and medical doctors. Much of the confusion comes from differing sunscreen regulations around the world, and the fact that “not safe” has different meanings in everyday, regulatory and toxicological contexts.

This is part 2 of my articles responding to the Huberman Lab podcast’s skincare episodes. Thanks to toxicologist and cosmetic safety assessor Mo Skin Lab for his feedback and factchecking of this section of my script! The video version is here.

Relevant experts

Andrew Huberman (AH): So I do believe in certain sunscreens, meaning I will put sunscreen on on certain days on certain parts of my body. However, I do believe now having spoken to multiple dermatologists and looked into the literature very deeply that there are certain chemicals in certain sunscreens that are of concern.

Given the option, we should opt for the healthier choices. And in fact, there are known healthier choices. To make all of this very clear. I’m going to tell you what is very clear to the dermatology community at this point in time.

There are a lot of problems here, and the overarching one is relevant expertise. Huberman is a neuroscientist and he’s talked to dermatologists, but these aren’t the most relevant scientific backgrounds for understanding sunscreen safety.

This might be surprising to some people – a lot of topics related to skincare are not dermatology. Dermatologists are medical doctors who mostly treat skin disease, and it’s a far more complicated discipline than you’d expect from seeing dermatologists on social media and in news articles. Dermatology training has a lot of serious medical things to cover that are needed for practicing as dermatologists – there’s not that much time or need to cover, say, what moisturiser ingredients do (which we’ll get to in a later part), or how shampoo works (we’ll also get to that)… or ingredient safety.

Safety assessments

Ingredient safety is the expertise of a whole different set of experts. The main ones are safety assessors, who are usually regulatory toxicologists. Other common backgrounds involved include pharmacy, dermatology, chemistry and even veterinary science. Risk assessment is a very narrow specialty within those fields, so they generally have higher toxicology-specific degrees on top of that training. Most pharmacists, dermatologists, chemists and veterinarians probably don’t even know this process exists!

Sunscreens are regulated as drugs in the US, Australia and Canada, and undergo a stringent approval process. Individual active ingredients are assessed for safety by regulatory toxicology panels. These assessments aren’t usually published in the peer-reviewed literature (they’re essentially government reports or “grey literature”). In many other regions like the EU, Korea, Japan and Brazil, sunscreens are a special category of cosmetics which get more scrutiny – again, many official safety assessments.

These assessments consider peer-reviewed studies, as well as a lot of data outside of the scientific literature, and they don’t simply read studies and take their results at face value. I’m sure Huberman thinks he “looked into the literature very deeply”. But in a safety assessment, toxicologists choose specific data points after assessing their validity and relevance, then use them in calculations and toxicological models to predict what’s safe. This is a very different level of scientific appraisal and interpretation!

Expertise is specific

This isn’t me dismissing dermatologists’ expertise – the reality of expertise is that it’s specific, and it takes a lot of time to build. It already takes over 10 years to become a dermatologist. To be a safety assessor you need a relevant degree, like toxicology or pharmacy or medicine. Most also have a more toxicology-specific masters or PhD, then there’s professional training on how to conduct safety assessments in your region to comply with local regulations. This is a total of maybe 7 to 10 years of training.

I’m sure there’s someone out there who’s gone through both sets of training, but the vast majority of dermatologists are not experts in regulatory toxicology, and vice versa.

My friend Jen of The Eco Well made this chart on the right experts for different topics (her podcast features many interviews with different cosmetic industry experts):

I tried to raise the issue of relevant experts in a comment on Huberman’s Instagram post, so maybe he would consider other sources before talking more about sunscreen. But he seemed pretty convinced that his “Harvard trained derm expert in oncology” would be an appropriate expert for the topic:

About a month later we got the second episode, with board-certified dermatologist Dr Teo Soleymani who specialises in surgery. His statements on sunscreen matched the first episode, so I’m guessing he was the main source. 

Staying in your lane?

Don’t get me wrong – I’m not saying we need to gatekeep, or experts need to stay strictly within their lanes and not talk about anything else. I mean, my background is medicinal and supramolecular chemistry, but I cover a lot of topics outside of that (UV scattering in part 1 is mostly physics. I’m about to talk about toxicology, which has a lot of overlap with medicinal chemistry, but it’s not the same). Most general interest topics involve more than one area of science, and communicating science clearly and accurately is a lane in itself.

But the further you go outside your area of expertise, the more you need to check if your understanding is correct, which involves consulting relevant experts.

A big problem is you don’t know what you don’t know. And a lot of people, including many dermatologists and scientists, don’t know these regulatory processes that ensure consumer product safety even exist.

Chemical sunscreen safety

In the first episode, Huberman has a 10 minute section about chemical sunscreens:

AH: When it comes to chemical based sunscreens, personally, I avoid them…

The main gist is that mineral sunscreens are safe, but chemical sunscreen safety is debated:

AH: But there are these concerns about some of those chemical components as endocrine disruptors and potentially as mutagens.

AH: You can find all sorts of concerns out there on the internet. Most of those concerns are not substantiated, but these chemicals can be problematic at high concentrations.

FDA studies

Dermatologist Dr Teo Soleymani goes into more detail about the specific concerns. He starts by saying he tends to only recommend mineral sunscreens, then gives his reasons:

TS: In the original set of sunscreens that were approved by the FDA that came out in 1999, there wasn’t enough data to look at biologic effects, efficacy, internal organ involvement, et cetera. Fast forward 20 years and we’ve gathered a lot more information about these chemical organic compounds.

There was an amazing 2020 study that looked at absorption of chemical sunscreens when they’re applied onto the skin […] even with single application, they saw blood plasma absorption of these chemicals that were 100 to 500 times greater than the upper threshold defined by the FDA.

Now the question exists: OK, what does that mean? That’s still up for debate.

This is a common misunderstanding of what the FDA studies mean (I’ve seen many medical doctors say something similar). I think much of the confusion is because we’re not just discussing science – it’s also regulations and laws, which don’t necessarily reflect the scientific understanding. (Note: The regulatory situation can also rapidly change, so while this was correct to the best of my knowledge at the time of writing (December 2024), it may not necessarily be correct by the time you read this!)

Related post: Sunscreens in your blood??! That FDA study

The FDA’s “upper threshold”

The FDA published two studies on sunscreens absorbing into blood in 2019 and 2020. Before then, the regulations operated on the assumption that sunscreen ingredients weren’t absorbed into blood at higher than half a nanogram per millilitre (0.5 ng/mL). This is “upper threshold” Soleymani was referring to when he said “100 to 500 times greater than the upper threshold”, but I’m not sure he really understands it given how he talks about it:

TS: That 2020 study that showed that we’re seeing it in the blood at levels that are 200 to 500 times the upper limit of normal as defined by sunscreen criteria.

This sounds really scary, but 0.5 ng/mL isn’t the “upper limit of normal” – it’s actually a very low limit called the Threshold of Tocicological Concern. It’s low enough that the FDA assumes it’s safer by default.

This is explained in the FDA study they cited: “plasma concentrations that surpassed the FDA threshold for potentially waiving some of the additional safety studies for sunscreens”.

At this low a level, there simply aren’t many molecules in your blood, even if they potentially accumulated in your body. Other types of data already show these ingredients are extremely unlikely to have harmful long term effects at these levels (we can’t say they definitely won’t – scientists hate committing to extremes – but it is a very conservative limit). So ingredients in blood at below 0.5 ng/mL don’t need more detailed safety studies to get approved.

This is explained in the first FDA study: 

“The 0.5-ng/mL threshold is based on the principle that the level would approximate the highest plasma level below which the carcinogenic risk of any unknown compound would be less than 1 in 100 000 after a single dose […] Application of this concept was considered acceptable during the determination of the “generally recognized as safe and effective” status of sunscreen active ingredients because such ingredients will be supported by extensive human use and absence of other pharmacologic or toxicologic signals from the nonclinical assessment recommended in the FDA sunscreen guidance.”

You can imagine that there’s a complicated flow chart for sunscreen active approval. There’s a fork for whether the blood concentration is above or below 0.5 ng/mL. Because they were thought to be below 0.5 ng/mL, US chemical sunscreen ingredients went down one path – this eventually led to them being classified as Generally Recognised as Safe and Effective (GRASE).

These two studies were a big deal, because they meant the FDA officially recognised that chemical sunscreens should go down the other path. So in 2021, the FDA’s new proposed order (not yet in effect) indicated that specific safety studies on humans and animals were needed for GRASE (re)approval. There was no reason to do these tests before, so the data doesn’t exist yet.

This might not sound like a huge problem – get the data and they’ll be approved again – except, again, regulations.

Here’s where the fact that sunscreens are sometimes cosmetics comes in. Testing cosmetic ingredients on animals is banned in many places like the European Union, where bans have been progressively introduced since 2004. More bans have been introduced in other regions as well.

The studies the FDA needs are specific and expensive, and the ingredient manufacturers who would fund them sell sunscreen ingredients worldwide. This means manufacturers essentially have to choose between doing the studies for the US, or not do the studies and keep selling them elsewhere. More and more animal testing bans are happening, so they’re probably going to choose the rest of the world. There’s a decent chance the US won’t have chemical sunscreens at some point (more on this mess in this sunscreen conference I cohosted with Jen of The Eco Well.)

Is sunscreen safe?

TS: Now the question exists, okay, what does that mean? Is this healthy? Is this not healthy? Is it neither? That’s still up for debate.

This is pretty much the official regulatory position in the US – “without this new data we don’t know if they’re safe”. But that’s not the scientific position.

Related post: More Sunscreens in Your Blood??! The New FDA Study

In the rest of the world, sunscreen regulations are different – essentially, the approval flow charts and the specific data needed aren’t the same. (Side note: regulations not matching science is also why US sunscreens don’t have the newer chemical filters that make European, Asian and Australian sunscreens so much nicer to use.)

The rest of the world has recognised that sunscreens absorb into blood and assessed safety accordingly for decades. In fact, studies suggesting sunscreens exceeded the FDA 0.5 ng/mL threshold date back to the 1990s. US people aren’t built that differently from other people (probably) – “no one knows if sunscreens are actually safe” is a legal fiction.

We can always use more precision and there’s always more data to collect (for any field of science, really). But how much we don’t know is massively overblown.

Non-US sunscreen safety assessments

The EU started reassessing chemical sunscreen safety in 2021, focusing on the older chemical sunscreens with the most cause for concern (mostly possible endocrine disruption). The chemical sunscreen ingredients commonly used in the US have been reassessed as safe.

I went through the EU’s safety assessments in a lot of detail in this post (which was checked by 3 toxicologists). The high level overview:

• The safety assessors went through all the hazard data on how the ingredient could be potentially harmful, including animal and human studies. They decided on the point of departure (PoD), a dose that’s expected to cause little to no harm (in most assessments so far this is the No Observed Adverse Effect Level or NOAEL).
• Then they went through all the data on exposure: how much actually gets into our bodies. Considerations include how easily it goes through skin, how much you apply, how you apply it (e.g. a spray would be inhaled AND absorbed through skin), if you’re likely to apply it in more than one product. For sunscreen, they generally go with a very high level of use e.g. full body application every day, much more than most people use.
• From these two values, they calculated the level allowed in sunscreen so you’d only get 1/100th of the amount that should cause little to no harm. This isn’t the full amount that should cause little to no harm, but 100 times less! This huge buffer is called the margin of safety.

For example, oxybenzone was allowed at 6% in EU body sunscreens, but this was lowered to 2.2% in 2021. This doesn’t mean the EU’s safety committee thinks 6% is bad for you – it means they calculated that 220% should still not be harmful to your health, applied to your entire body daily.

Related post: US Sunscreens Aren’t Safe in the EU? The Science

Regulatory activity is constantly making sunscreens safer and safer in the background. Currently, Australia’s TGA is working on a new approach to sunscreen assessments that should be published in early 2025.

Sunscreens are very safe, and are being made safer

This is why both Huberman and Soleymani are incorrect about how uncertain all the data is:

AH: Some of that fear is substantiated when one goes and looks at the studies…

AH: The way these studies were done often involves having people apply a ton of these chemical based sunscreens […] A big issue that’s not often discussed because it’s very difficult to control for in a natural setting, but is straightforward to control for in a laboratory setting, is how much sunscreen one is applying and how often and across how many years of time. So there’s no real prescriptive that can tell you, hey, if you put chemical sunscreens on once, that’s problematic.

TS: There’s data that suggests that the chemicals are found in breast milk, amniotic fluid, blood plasma, urine. So there’s a lot of things that we don’t know. And I always say this in science: we take two steps forward and then maybe one step diagonally or sideways because we ran into unexpected things. I tend to recommend mineral sunscreens because they don’t have any of that data.

If you’re just looking at peer-reviewed sunscreen studies without understanding the underlying science and regulatory processes, it might seem like there’s human blood and urine measurements, high dose rodent and zebrafish experiments, and changes in in vitro cell studies – so the real risk is somewhere within this massive range.

But the realistic range is much smaller, because these data points feed into toxicological models that can make pretty accurate predictions. It’s like how no one had ever sent a telescope as big as the JWST into space before, but because data points like weight and fuel efficiency, and physics models that can make accurate predictions, it was successful.

Even though it might look really uncertain if you’re looking at the individual puzzle pieces, safety assessors know the big picture and how everything fits together. And while there are uncertainties, they’re nowhere near as big as they were made out to be in these episodes.

The Environmental Working Group tends to amplify these uncertainties and highlight concerning data, but if you understand how it feeds into safety assessments, the data is actually very reassuring. I personally wasn’t too concerned about chemical sunscreens, but I did wonder about potential impacts for developing fetuses and if pregnant people should avoid particular products. But after reading the safety assessments properly, my mind was really at peace – I highly recommend reading this post, and perhaps a full safety assessment for yourself.

References

Matta MK, Zusterzeel R, Pilli NR, et al. Effect of sunscreen application under maximal use conditions on plasma concentration of sunscreen active ingredients: A randomized clinical trial. JAMA. 2019;321(21):2082. doi:10.1001/jama.2019.5586

Matta MK, Florian J, Zusterzeel R, et al. Effect of sunscreen application on plasma concentration of sunscreen active ingredients: A randomized clinical trial. JAMA. 2020;323(3):256. doi:10.1001/jama.2019.20747

D’Ruiz, C. US Sunscreen Landscape. 2023 Sunscreen E-Summit. May 7, 2023.

Farina, A. Regulatory Update. 2023 Sunscreen E-Summit. May 7, 2023.

US Food & Drug Administration. Questions and Answers: FDA posts deemed final order and proposed order for over-the-counter sunscreen. December 16, 2022. 

Hayden CG, Roberts MS, Benson HA. Systemic absorption of sunscreen after topical application. The Lancet. 1997;350(9081):863-864. doi:10.1016/S0140-6736(05)62032-6

Scientific Committee on Consumer Safety, SCCS Notes of Guidance for the Testing of Cosmetic Ingredients and their Safety Evaluation 11th revision, 2021.

Scientific Committee on Consumer Safety, Opinion on Benzophenone-3, 2021.