Nanotechnology in sunscreen unlikely to be toxic: Australian study

An Australian study has provided the first direct evidence that nanoparticles in sunscreens cannot penetrate the skin, as has been claimed by advocacy groups.

The small study, by University of South Australia and University of Queensland researchers, found zinc oxide nanoparticles dissociate into ions when applied to the skin, meaning it is unlikely these sunscreens enter the bloodstream.

Nanoparticles in sunscreen should not be feared, according to a new Australian study.Credit:Stocksy

Nanotechnology has become a popular feature of physical sunscreens, the name given to sunscreens which contain a metallic ingredient like zinc oxide or titanium dioxide to reflect UV rays (as distinct from chemical sunscreens, which absorb the rays).

By using nanoparticles of these ingredients, the products appear transparent on the skin, instead of leaving a white residue.

Some advocacy groups, particularly in the wellness space, have expressed wariness around nanoparticle use in sunscreens, citing the effects of stem cell culture studies and animal studies.

However, there has always been little evidence to support that this is how sunscreen behaves when being applied to human skin. A 2014 laboratory study jointly conducted by the CSIRO and a number of local research institutions found nanoparticles in sunscreen, if able to enter the skin, would be broken down by the immune system before they reached the blood stream.

University of Queensland researcher Dr Yousuf Mohammud said the results of the new study, the first of its kind on humans, is not inconsistent with this prior laboratory finding.

"What our study's shown is that, if you apply zinc oxide, it gets dissociated into zinc ions," he explained. "So, the question of the immune system taking care of the nanoparticles doesn't arise here because the nanoparticles don't get inside the skin intact."

While he said the research, which was published in the Journal of Investigative Dermatology in November, did not definitely conclude the same was true of titanium dioxide nanoparticles – which dissociate more slowly than zinc oxide ions – it seemed likely there would be a similar result if these nanoparticles were tested.

"If they are about the same size, then they will not go in the skin, like we found," he said.

Heather Walker, chair of the Cancer Council's national skin cancer committee, said the study "adds to the body of evidence that we have nanoparticles in sunscreen are safe".

"We know that sunscreens prevent cancer and particularly the deadliest form of skin cancer, melanoma, and we know that they're safe," she said.

Consumer confidence in sunscreen use has been on the decline. The Cancer Council's 2017 National Sun Protection Survey found only 55 per cent of Australians believe sunscreen is safe for use every day, down from 61 per cent in 2014.

Seventeen per cent of survey respondents said they believed sunscreens contained ingredients that are bad for your health.

University of Sydney dermatologist, and Australasian College of Dermatologists spokesperson, Associate Professor Stephen Shumack said consumers should be confident in using sunscreens with zinc oxide or titanium dioxide nanoparticles, citing the two reviews the Therapeutic Goods Association (TGA) have performed on nanoparticle sunscreens in the past decade.

"[The TGA] have come down saying there's no evidence that nanoparticles have any adverse affects, if they're used in sunscreens on normal skin," he said. "Now, that's not to say there might be some issues if you're putting sunscreen on broken skin, but you shouldn't really be doing that anyway."

As a dermatologist, Associate Professor Shumack said he would "definitely" recommend sunscreen use, stating that often the skin problems people might cite as making them less likely to wear sunscreen can be easily solved by opting for a sunscreen with a different base.

"For instance if people have a tendency towards acne, they want to avoid using the ointments, thicker and greasier products, and instead use more lotions or gels or milks – those sort of runny products which are less likely to block up the skin and less likely to make acne or problem skin worse," he said.

"Alternatively, people who might have dry skin, as caused by eczema or dermatitis, might like to use a thick cream or ointment because that provides a moisturising effect on the skin as well."

'New issues' with misinformation every summer

The Cancer Council recommends wearing seven teaspoons of sunscreen with an SPF of at least 30+ and reapplying every two hours or after swimming on days when the UV index is at three or higher.

Associate Professor Shumack said he would tell people to instead opt for SPF 50+, given so few manage to use seven teaspoons of product on each application.

According to Walker, the Cancer Council organisation faces "new issues" with misinformation about sunscreen use every summer.

"There are five sun protection measures and those are slip, slop, slap – clothing, sunscreen, hat – shade and sunglasses, and we always recommend using them in combination," she said, adding sunscreen use is often characterised by inadequate application or an overreliance (i.e. using sunscreen as a standalone defence).

Product trends also create challenges. Walker warned against the use of aerosol sunscreen sprays, saying they have been discontinued from the council's own sunscreen range because it is nearly impossible to apply the needed amount for protection.

"No one is getting the SPF advertised on the packaging," she said. "People are spraying them like insect repellent so they are not using enough and, if it's a windy day, half of the product is flying down the beach."

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