Sunscreens and Alzheimer’s – solid science or scare-mongering speculation?

Could using sunscreen lead to Alzheimer’s, Parkinson’s, or other neurodegenerative diseases?  The association seems far-fetched – given the amount of sunscreens, creams and lotions used every day, surely someone would noticed a link by now if it existed!  Yet a press release from the University of Ulster suggests the nanoparticles used in some sunscreens could potentially cause or exacerbate these diseases.  Drawing on the release, a number of media outlets are now running stories along the lines of “Sunscreen could cause Alzheimer’s” (this from The Daily Mirror in the UK).

This is a rather unfortunate case of a poorly conceived press release leading to sensationalist – and misleading – headlines… The press release is associated with new research funded under the umbrella of NeuroNano – a European project focused on developing nanoscale neuro-implants that will enhance the functioning of the brain.  However this new project, being led by Professors Vyvyan Howard and Dr. Christian Holscher at the University of Ulster, is focusing on how nanomaterials inadvertently entering the brain could cause damage.

The basis of their research is actually quite reasonable.  There is some evidence that exposure to specific types of nanometer-scale particles could lead to them entering the brain, either by traveling up the nerves connecting the nose to the brain, or by crossing over from the blood.  If insoluble nanoparticles do get into the brain they are likely to stick around for a while, as there are limited ways in which the body is able to get rid of foreign material from here.  While there, they could damage neurons by causing the release of reactive oxygen species (ROS) – highly active chemicals.  And there is also research showing that some nanoparticles can cause the type of protein misfolding that has been associated with neurodegenerative diseases like Alzheimer’s – although this was carried out outside the body, under conditions set up to favor misfolding.

These tantalizing snippets of information are like a red rag to a bull as far as scientists go – they suggest there is new knowledge waiting to be discovered; knowledge that could help prevent some forms of brain disease.  Together, they form a sound reason for carrying out more research.

But in no way do they link sunscreens to Alzheimer’s!

The sunscreen link comes about because a number of these lotions use insoluble nanoparticles as the active ingredient.  The thought-process then goes something like this:

The nanoparticles of titanium dioxide or zinc oxide in a sunscreen could conceivably get into someone’s body, by passing through the skin, being eaten, or being inhaled.  Once there, they might be able to get into the blood.  From there, there is a chance that they could pass over into the brain.  Or they might even be inhaled and travel straight up the olfactory nerve and into the brain.  And once there, they could cause vital proteins to misfold that then lead to diseases like Alzheimer’s.

But while this makes an interesting story and a compelling grant proposal, it has little bearing on reality as we currently understand it:

  • Most research suggests nanoparticles in sunscreens don’t pass through the skin.
  • Even if you could snort sunscreens (a feat in itself), studies showing nanoparticles traveling from the nose to the brain have used rodents not humans – and human noses are very different; they don’t offer the same opportunities for significant exposure through this route.
  • It takes a very special type of nanoparticle to cross the blood-brain barrier – you can’t get any old junk across it.
  • And research into nanoparticle-induced protein misfolding is at a very preliminary stage – any associations between effects seen in test tubes and brain disease are little more than speculative.

More to the point, we are exposed to billions of nanoparticles each day in the air we breathe; from car exhausts, fires, even sea spray.  If any nanoparticles are going to find their way to our brains in large numbers, it will be these – not those used in some sunscreens.

This is not to detract from the importance of this new research project.  If there are links between nanoparticle exposure and neurodegenerative diseases, we need to know.

But linking sunscreens to Alzheimer’s in the absence of any hard scientific data?  Given what we currently know, that just seems irresponsible!

Update, 8/27/09.  Since posting the original press release, the University of Ulster have changed the headline – without, apparently, telling anyone.  What was “Groundbreaking Research Links Sunscreen and Alzheimer’s Disease” is now “Groundbreaking Research Into Nanoparticles And Alzheimer’s Disease.”

Makes you wonder how much of the sensationalist coverage could have been avoided with a bit of forethought, rather than post-thought.

Thanks to @silentypewriter for the archive link

For more information…

Information on the NeuroNano program can be found here

Nanoparticles traveling from the nose to the brain: There have been a number of studies showing that this is possible in rodents, although little is known about how many particles are likely to get to the brain after being inhaled.  Three useful papers are:

Oberdörster, G., Z. Sharp, V. Atudorei, A. Elder, R. Gelein, W. Kreyling and C. Cox (2004). “Translocation of inhaled ultrafine particles to the brain.” Inhal. Toxicol. 16(6-7): 437-445.

Elder, A., R. Gelein, V. Silva, T. Feikert, L. Opanashuk, J. Carter, R. Potter, A. Maynard, J. Finkelstein and G. Oberdorster (2006). “Translocation of inhaled ultrafine manganese oxide particles to the central nervous system.” Environmental Health Perspectives 114(8): 1172-1178. [PDF]


Oberdörster, G., V. Stone and K. Donaldson (2007). “Toxicology of nanoparticles: A historical perspective.” Nanotoxicology 1(1): 2 – 25.

For information on nanoparticles and protein misfolding, the following is a key paper:

Linse, S., C. Cabaleiro-Lago, W.-F. Xue, I. Lynch, S. Lindman, E. Thulin, S. E. Radford and K. A. Dawson (2007). “Nucleation of protein fibrillation by nanoparticles.” Proc. Natl. Acad. Sci. U. S. A. 104: 8691-8696.

The Mexico City study mentioned in the University of Ulster press release is:

Calderon-Garcidueñas, L., B. Azzarelli, H. Acune, R. Garcia, T. M. Gambling, N. Osnaya, S. Monroy, M. R. DEL Tizapantzi, J. L. Carson, A. Villarreal-Calderon and B. Rewcastle (2002). “Air Pollution and Brain Damage.” Toxicol Path 30(3): 373-389.

When it comes to crossing the blood brain barrier, there has been a lot of research on engineering nanoparticles to do exactly this – for delivering drugs.  Most research has shown that fancy materials science and chemistry are needed to engineer nanoparticles to move across the barrier – it’s pretty effective at keeping bad stuff out of the brain.  However, there are indications that small quantities of very small nanoparticles could inadvertently cross over from the blood – more more research is needed to understand whether early findings have any significance though.

Less is known about the possibility of ingested nanoparticles getting into the bloodstream.  Again, the barrier between the guts and the blood is a complex one, and it is unlikely that any old nanoparticle will be able to fool the body into getting where it isn’t wanted.  But this is an area where more research would be useful.

For more info on nanoparticles and sunscreens, check out Industry critics give nanotechnology sunscreens the thumbs up

For more papers on nanoparticles and the brain, check out the nanoEHS Virtual Journal

11 thoughts on “Sunscreens and Alzheimer’s – solid science or scare-mongering speculation?”

  1. Andrew: Upon reading the news article, my first concern exactly was the same as yours. A news article about a department receiving research funding to explore a hypothetical link (as yet hypothetical) is headlined to make it look like a causal or direct contributory link exists! I used to for a long time write a headline-debunking blog on obesity related research. Your post makes me wonder if I should resume. Thanks for writing about this!

    1. I’m afraid in this case the University of Ulster press office isn’t blameless. With a press release having the title “New Research Investigates Link Between Sunscreen and Alzheimer’s Disease” you have to wonder, “what they were thinking?!”

  2. I agree with most of your arguments. However, you nearly lost me when you wrote, in the first paragraph no less, that “The association seems far-fetched – given the amount of sunscreens, creams and lotions used every day, surely someone would noticed a link by now if it existed!” This is not a valid criticism in any context, I believe, and especially in this particular one which involves long term exposure and a degenerative disease that may take decades to manifest.

    1. Hi Delia,

      My apologies – I was aiming to be superficially provocative with that sentence, but from your comments I may have misjudged it! This wasn’t meant to be a criticism or even a direct statement or conclusion: I wanted to reflect an intuitive lay response to apparent news that a reasonably common product could be linked in a hitherto unnoticed way to a serious condition – while including enough qualifiers to prevent the sentence from reading like a definite statement. Clearly trying to be too clever by half!

      You do raise an important point, and one I don’t tackle in the piece – that it’s dangerous to be dismissive when dealing with a poorly understood degenerative disease. It is not beyond the realms of possibility that the particles used in sunscreens and elsewhere could be linked with neurological diseases, which is why the research is justified. However, my contention here is that given the current balance of information, it is dangerous to draw associations where no justification yet exists.

  3. I am a total dilettante in science, and these news made me feel scared,.
    Your article calmed me down a bit, but some questions remain. You said: “the barrier between the guts and the blood is a complex one, and it is unlikely that any old nanoparticle will be able to fool the body into getting where it isn’t wanted. ”

    May I ask, what does “old nanoparticle mean”? Forget the sunscreens, many cosmetic companies boost that their fluids or eyeshadows contain particularly modern high-tech nanoparticles, what can be said about this? What can be said about titatium dioxide added as an “inactive ingridient” to common pills, is it safe, just because this titanium dioxide was not especialy engineered?..

  4. I can see I’m pretty late to this discussion, but I feel my questions are still worth asking.

    Firstly, you claim “studies showing nanoparticles traveling from the nose to the brain have used rodents not humans – and human noses are very different” to support your argument that in this context, these sunscreens are more likely to be safe to humans than rodents. As a human, I take some comfort in learning this.
    Furthermore, the nanotech industry claim that these new nanotech compounds are more stable than previously….surely a good thing as well, given that my tube of sunscreen can sit on my shelf for months or even sometimes years.

    My question then is – If we probably don’t absorb these nanoparticles of zinc and titanium dioxide etc., where do these compounds go after we have rubbed them onto our skin?
    Surely the answer must be into our surrounding environment?
    Into the water (if we’re swimming), onto the grass or sand if we’re sunbaking, and also onto our clothing, and therefore into the sewage and ultimately our creeks, rivers and oceans.
    So, isn’t it also important if these nanoparticles CAN pass into rodent’s brains? Perhaps many people don’t love rodents (especially those that experiment on them), but what about their own pets? Or smaller aquatic invertebrates and microorganisms? Have these safety tests been performed satisfactorily?

    That leads me to my second point.
    You rightly make the point “If there are links between nanoparticle exposure and neurodegenerative diseases, we need to know.”
    So, if we don’t know exactly what the long term/chronic effects of many nanoparticles, such as those in our sunscreens as you suggest – how is it okay that the nanotech industry has been allowed to release them onto our shelves and ultimately into our environment?
    I have used sunscreen all my life under the harsh Australian sun, and it seems to have been pretty good at protecting me from burns – when used correctly. I would have been fine waiting another decade or more for real long term safety tests to be performed on the nanoparticles in sunscreens before their release.
    What’s the huge rush….?

    1. Thanks for the comments Gregory.

      First, your question on where the particles go is a crucial one – especially where the particles aren’t that biodegradeable, like the TiO2 nanoparticles, and so may persist for some time in the environment. There are an increasing number of research groups around the world that are beginning to look at this question – as well as asking what the possible environmental impact might be. At this stage, it isn’t clear whether there are legitimate concerns or not, but it seems the potential is there for averse impacts if we are not careful. (The same goes for the release of non-nano sunscreens into the environment of course, although here the concerns are more related to the direct impact of the the chemicals used in the sunscreens, rather than persistent and possibly photoactive nanoparticles).

      I should also add that understanding potential exposure routes is important. I would imagine that sunscreens that are washed off the body will not present a significant inhalation exposure to mammals. But there will be other groups of organisms that come into contact with them through ingestion and other uptake routes.

      Your second question is a little more difficult to answer, and really taps into the whole business of innovation, economics, profit and progress. In this short comment, I think the best I can say is that halting “progress” until we know all there is about the safety of a product is unlikely to work (because of social, economic and political drivers), but we do have the option of developing new products as safely as we can, and in finding innovative ways to bridge the uncertainty gap between new products/technologies and their potential impacts. And to be fair, in the case of sunscreens, there are some compelling arguments why you might want to use titanium dioxide and zinc oxide over other active ingredients, based on the current state of knowledge.

      1. I totally agree that the case for using Titanium dioxide and zinc oxide is strong, and do in fact use these types of sunscreens myself. Fortunately, thanks to some great work by Friends of the Earth here in Australia, I have the choice not to use brands of sunscreen containing nanoparticles.
        And of course you’re also correct that these non-nano sunscreens may also harm the environment, as so many chemicals we use in our world. However, we also agree that these are much less likely than their nano-scale equivalent.

        It seems that where we disagree, is that while research groups around the world begin to look at the all-important questions of persistence, photoactivity and toxicity – I maintain that we should insist that industry waits until more rigorous and long-term testing is performed. I simply not believe that most new products containing nanoparticles have been tested “as safely as we can”, so how can this argument be used to maintain that these nanoparticles should be approved for release. At the very least, we should insist on labelling such products, so that concerned consumers at least have a choice.
        I refuse to see this as halting “progress”, when effective sunscreens exist on our shelves without the need for nanoparticles.

        Your allusion to “social, political and economic drivers” opens up another whole kettle of fish. While the economic drivers are clear (i.e. industries must develop new products to adapt, expand and increase profits), could you please speculate on the social and political drivers behind the need for nanoparticles in sunscreen?

        1. Hi Gregory,

          I’m with you all the way on providing consumers with clear information on what is in the products they buy – obscuring information can only backfire in the end.

          In terms of testing, I would agree that more work is still needed to ensure that we are testing the right things – especially when it comes to factors like photoactivity. However, there are no bright lines here between what is sufficient and what is insufficient – meaning that the decision to use a material or hold off is going to be a (hopefully well-informed) judgment call. In the case of nanoscale TiO2 and ZnO, my position would be that the data we currently have puts us on the “proceed but with caution” side of the fuzzy line – others will disagree.

          Social and political drivers – a kettle of fish indeed! The social drivers include balancing skin protection and avoiding skin cancer with cosmetic “assurance,” ease of application, effectiveness, and avoiding adverse skin reactions. The non-nano sunscreens currently available are adequate in many cases, but certainly not perfect. A lot of this comes down to the market – is there a market for sunscreens that use alternative active ingredients?

          Then there are the political drivers. I may be getting into murky waters here, but given the high level of government investment in nanotechnology around the world, there is a strong incentive to highlight nanotech success stories, and to avoid appearing to signal that some uses of nanotech are dangerous or ill-regulated. These are subtle drivers – but when you think of the fuzzy line I mentioned above between promoting or holding back on the use of nanoparticles in sunscreens, which side of that line do you think that a government investing rather a lot in nanotechnology would prefer to fall?

          There’s also another sociopolitical driver which is more obvious in Australia – the desire find effective ways to tackle skin cancer associated with sun exposure. Again, the decision to act decisively in the face of fuzzy information comes down to a political decision – which technologies do you back, and how do you promote their use?

          1. Hi Andrew,

            again, you make some really good points!

            Many governments of the world (including here in Australia) have indeed placed themselves in a very messy and murky situation relating to this conflict of interest you allude to. This conflicting desire for governments to generate returns on their investments and generally not “stifle progress” on one hand, whilst also having the responsibility for safe-guarding their citizens and (supposedly) the environment on the other – does not inspire any confidence or trust in nanotechnology safety to me at all.

            You may also well be right is suggesting that in the long run, the nanoparticles in sunscreen will probably not end up significantly harming humans or our environment. I really, really hope you are.
            And given that these particles are already being released into our environment and no government seems intent on banning or regulating further use until more comprehensive safety tests are complete, we’ll just have to wait and see what happens in coming years as to whether they were right to do so….

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