Zinc Hunting – The Nano Sunscreen Diaries

Last year I was one of the guinea pigs in a study looking at Nano zinc in sunscreens and skin penetration (you can read more about that here).   After the preliminary results were presented at a nanotechnology conference in Sydney earlier this year showing that small amounts of zinc had penetrated the skin interest in this area has been growing.  Government bodies, regulators, product developers and the public  want to know if the use of nanoparticulate zinc in sunscreens is safe – after all, the guys in Europe recently ruled that nanoparticles should be declared on labels as part of a ‘precautionary principal’ approach.  This labelling is not a requirement in Australia currently.

Anyway, in light of the growing interest in this are the Macquarie University published a statement recently aimed at re-iterating the findings and drawing a line under what we currently know and don’t know. 

Here is the unchanged statement (or read it on their website here):

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A technique developed by Macquarie University has proven for the first time that a tiny amount of zinc from sunscreens is absorbed through the skin into the human body, but is not yet able to discern whether the zinc is in nanoparticle form.

Professor Brian Gulson of Macquarie University conducted the research – published online in the current edition of the journal Toxicological Sciences – with collaborators in CSIRO and the Australian National University and the Australian Photobiology Testing Facility. The research was widely reported on in February 2010 following a presentation by Gulson at a scientific conference.

The team traced the skin absorption of a highly purified and stable isotope which allowed them to distinguish the zinc from the sunscreen from that which is naturally present in the body or environment. Zinc is absolutely essential to bodily functions.  

To simulate real life conditions, the team carried out the study outdoors over five days in March 2009. Two groups of males and females had sunscreen applied twice daily and blood and urine samples were collected and analysed for their zinc isotopic signature.

For the first time, the team found zinc from the sunscreens in the blood and urine of all volunteers, but one of the most interesting findings was that there was an increase in the tracer in the blood six days after the trial finished. The other important findings were that there was a linear increase in the zinc tracer with the amount of sunscreen applied to the backs of volunteers over the five days of the trial and there was slightly more tracer zinc in females who had a sunscreen with nanoparticles applied to those who had a bulk sunscreen applied.

In spite of these findings of definite penetration, Gulson said that: “the amounts of tracer zinc found in the blood were quite small (<0.001% of the applied dose) and would not add appreciably to the levels of zinc in the body, especially in light of the tight controls of zinc in people”.

At this stage, Gulson says that “the critical question of whether the zinc is present as nanoparticles or soluble Zn is unknown but under investigation”.

The researchers suggest that follow-up studies from the scientific community with different formulations over longer periods of time are essential, but that until evidence to the contrary is obtained, people spending time outdoors should continue to use sunscreens.

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So what does that mean for product developers?

Well, it is important that we (as a scientific community) carry out further work to find out what form the zinc that penetrates through the skin is in as that makes all of the difference.  The worry that surrounds nanoparticles comes from the fact that these ultra-small particles may  act very differently from their big brothers and sisters and may therefore need to be treated as different entities (they are often  more energetic and therefore catalyse reactions, something that is not desirable in this type of sunscreen).  However, I must emphasise that it is not currently known what form the zinc that penetrated during this study was in.

It is possible (and even very likely) that nanoparticles  form aggregates in the sunscreen meaning that zinc that penetrated in the nano-zinc suncreen may not actually be nano-sized any more.  This may sound like a long shot but it isn’t really. It is extremely difficult for a formulator to suspend nanoparticles into a sunscreen in such a way as to prevent ANY agglomeration.  What usually happens is that you end up with a suspension of small and uniform aggregates that are still fine enough as to be invisible to the naked eye but not small enough to cause cell damage. These primary aggregates may still be small enough though to penetrate the skin under certain circumstances.

Another probability is that the zinc that penetrated is in a soluble form. The solubility of zinc depends on a number of factors including pH (acidity or alkalinity) of the environment and temperature. Further, the zinc could end up in many different forms depending on the environment that it finds its self in.  The fact that the zinc found in the body could be in a soluble form is highly significant as that means that it is no longer a nanoparticle in the sense that everyone is raving about.

The fact that only tiny amounts got through in BOTH the nano and bulk sunscreen means that the advice to maintain sunscreen use is still valid.  If we are to talk precautionary principles I would be weighing up the number of people that I know who’ve had skin cancers removed VS the number that have been made sick by their sunscreen.

And what does it mean for beach bums?

Same thing really, keep using your sun cream, listen to your body and if in doubt, don’t go out (which sounds awfully boring and a tad unhealthy).  If you really DON”T want nanoparticles near you you can always opt for the old-style zinc sticks OR go for the chemical rather than physical sunscreen products.

I am sure that there will be more to come and when there is, I’ll tell you all about it.

Stay sun safe.