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Sunny Side Down

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Do people get more than what they ask for when they apply the new generation sunscreens to protect their skin from the blistering sun? The question that has echoed several times in the past one decade may not have a clear answer as yet with the pendulum swinging in both directions. But a recent study, by a team of researchers from the Indian Institute of Toxicology Research (IITR), in Lucknow, has some disturbing accounts to reveal.

The scientists from IITR (formerly Industrial Toxicology Research Centre), led by Alok Dhawan, found that a material, used in the nanoparticle form in some of the sunscreens hitting the market in the recent past can actually interfere with DNA present in the skin cells. Such changes can even lead to cancer. “The material — zinc oxide — otherwise a benign substance, seems to trigger some changes in the genetic material present in skin cells when it is in nanoparticle form,” said Dhawan. He was quick to add that the tests have been conducted only on laboratory human skin cells and that his team has not yet studied its effects on a living person.


Sunscreens use either zinc oxide or titanium dioxide as the principal ingredient as both the substances possess the ability to scatter visible light — the primary objective of the cream, quite commonly used by sports personnel such as cricketers. In the conventional form, both the materials have a serious drawback: they remain as white patches on the skin. This disadvantage can be tackled by reducing the particle size. When they are smaller than 100 nanometres (one nanometre is one billionth of a metre), they don’t leave any mark on the skin and yet retain the sun-blocking property. “Such nanoparticles are 10 to 12 times smaller than a human skin cell and can easily penetrate,” explained Dhawan.

Nanoparticles — a million times smaller than a pinhead — are being hailed as the promise of the future. They are expected to revolutionise a number of fields, ranging from agriculture to health care to industry. They can find applications in drug delivery, cosmetics, electronics, textiles and many others. Many of these applications have progressed beyond the research stage.

However, there are conflicting reports about the adverse effects. Regulatory agencies, including those in the 21 countries that have cleared manufacturing and selling nanoparticle-based consumer products, are not absolutely clear about the toxic potential of these nanoparticles. For instance, US Environmental Protection Agency (EPA) periodically reviews new studies available on nanotechnology materials to assess their safety with regard to human health as well as the environment.

“There are unanswered questions about the impacts of nanomaterials and nanoproducts on human health and the environment,” EPA said in its last Nanotechnology White Paper released in 2007.

On the other hand, in a 2006 review specifically on zinc oxide nanoparticles-based sunscreens, Therapeutic Goods Administration (the Australian regulator) concluded, “There is evidence from isolated cell experiments that zinc oxide and titanium dioxide can induce free radical formation in the presence of light and that this may damage these (skin) cells. However, this would only be of concern in people using sunscreens if the zinc oxide and titanium dioxide penetrated into viable skin cells. The weight of current evidence is that they remain on the surface of the skin and in the outer dead layer of the skin.”

The IITR study, however, has shown that even at low concentration zinc oxide nanoparticles can penetrate the outer layer of the skin.

According to Dhawan, the problem with current toxicology studies of nanoparticles is that most research groups test the materials on rat or mice skin. “These rodent skins are 10 times denser than the human skin, and hence the chances are lesser that the tiny particles could pass through,” he told KnowHow.

Besides, many studies have used the sun block creams in much higher concentration. As a result the pasted cream itself created a barrier to skin entry.

Dhawan said he, as a scientist, is not against using nanoparticles. “All I would say is, proper clinical trials should be conducted before they are allowed to enter the market.”

For him, caution is the key word when it comes to the use of nanoparticles in consumer products.

Sources: The Telegraph (Kolkata, India)

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