Australian study: Most effective nano-sunscreens might also be the most toxic                                                            by Aarti Kapoor

Australia — The most effective nanoparticle-containing sunscreens may also come at the cost of being the most harmful, according to an Australian study published online recently in Nature Nanotechnology.

Dr. Amanda Barnard, a scientist at the Commonwealth Scientific and Industrial Research Organisation (CSIRO), Australia, used computer simulation of titanium dioxide nanoparticles  known for giving sun creams their transparent texture — to conduct a one-to-one comparison of their efficacy, aesthetics and potential toxicity in sunscreens. 

The nanoparticles that were used in the study ranged from three to 200 nanometers in size. 

Based on this research, Barnard found that the size and concentration of nanoparticles that gave the best transparency (aesthetics) and sun protection (efficacy) also had the highest potential for producing free radicals, which can possibly damage tissues or DNA (toxicity). 

“Cannot have our cake and eat it too”

“We can conclude that we cannot ‘have our cake and eat it too’, and that a trade-off is necessary when choosing these types of products,” Barnard said. 

“If we minimize the potential for free radical production then this comes at a cost of reducing the sun protection factor … which can increase the risk of damage from ultraviolet rays. Alternatively, maximizing the sun protection factor comes at a cost of increasing the potential for free radical production,” she explained.

However, Barnard pointed out that these results are not indicative of something that should raise concern, but offer a new and useful tool that manufacturers may use as a guide to optimize their products to meet the needs of consumers. 

Nanoparticles less than 13 nanometers — the most desirable?

Interestingly, the study noted that only particles less than 13 nanometers in size presented the minimal potential for toxicity, while being the most functional in their ability to block ultraviolet light and retain transparency. 

“This study does indicate that perhaps this is the size we should be focusing on,” Barnard said. 

However, she cautioned against concluding that all particles under 13 nanometers in size would be free of potential risk. “Nanoparticles less than 13 nanometers in size still need to be thoroughly tested by researchers in the field of nanotoxicology,” she said.

Environmental impact of sunscreen nanoparticles

Athough the model used in this study included a number of environmentally relevant parameters, further studies on the environmental impacts of nanoparticles in sunscreens are still required.

In this case, ambient temperature and pressure were used, and the nanoparticle size, shape and crystal structure were allowed to change in response to water interacting with the surfaces. The environmental stability was then mapped using a technique known as Thermodynamic Cartography. 

“This alone is insufficient to determine the environmental impacts …, but it does help us get one step closer, since the same free radicals are released into the environment when these sunscreens wash off,” Barnard said.

Trade-off

So until further research sheds more light into the potential risk of using nanoparticles in sunscreens, it seems that a consumer may just have to exercise some caveat emptor in this matter. In short, a trade-off may be necessary when choosing sunscreens. 

“Like all things in life, consumers need to make their own trade-off, and decide which of the multitude of products on the market best meet their needs. The sunscreen that is right for one person, may not be right for another,” Barnard said.  

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