Using nanoparticles in sunscreens safely Nicola Popplewell — P & C Review September 2010 Prof Johann Wiechers recently spoke at the Society of Cosmetic Chemists’ (Coschem) annual conference about the use of nanoparticles in sunscreen. His research into the safety of using these particles in formulations has revealed that while nanoparticles might not penetrate the skin, smaller particles such as quantum dots may be able to.   ‘Cosmetic formulators have been using nanoparticles in sunscreen products for the last two decades,’ says Wiechers. ‘Because nanoparticles allow for better transparency of the film on the skin, ingredients such as titanium dioxide and zinc oxide are common in many sunscreen formulations.   ‘Recently, organisations representing the general public’s interests have issued warnings about the dangers of nanotechnology, in particular about those nanoparticles that are frequently used in cosmetics: zinc oxide and titanium dioxide. In order to cause these detrimental effects, they have to penetrate into the living skin layers, but do they really?’ In the past few years, the number of commercial cosmetics products containing nanoparticles has risen dramatically with many of the big cosmetic players launching ranges utilising this technology. As the number of products on the market increase, concern regarding the side-effects of long-term use of these products also increased. ‘Everything is toxic. Water can be toxic if one consumes more than the human body can handle. What is important is to note the dosage. In order to determine toxicity, one needs to look at the exposure versus the hazard,’ says Wiechers. In his model, exposure looks at issues such as the product type, the amount of penetration and the waste streams, as well as how long the product was applied to the body. Hazard is determined by how much of the product needs to be absorbed before it affects the skin and what the affect is.   ‘2007 was the turning point for research in the penetration of nanoparticles. Before then, nanoparticles had not been proven to penetrate deeper than the stratum corneum. Scientists believed that the infundibulm (space around the hair inside the hair follicle) would act as a reservoir; nanoparticles would accumulate there until they were removed along with the skin’s sebum. However, not all scientists agreed and many papers were published that argued against this train of thought.’   After 2007, research into nanotechnology began to play with the idea of ‘quantum dots’. A quantum dot is a type of ‘nanoparticle’ that is smaller than 10nm in diameter. Due to the particles’ size and coatings, such as ionic charges, it is assumed that they are more likely to penetrate into the skin.   However, testing the exact affect and amount of penetration of these particles has proven difficult. For example, they have to be applied at a pH level of 8 in order to see any evidence. ‘Although much research has been done on these particles, the different experimental methods mean that there is no substantiated data available and therefore the likelihood of negative side effects from this particles cannot, or hasn’t, been determined,’ says Wiechers.   ‘Something else that needs to be taken into consideration when evaluating the safety of these particles are the real life conditions they will be used under, such as their inclusion in different formulations.’   Other real life situations that can affect penetration include UV radiation, which has shown that in some instances particles do penetrate but has yet to be adequately proven. ‘The skin is also not static; it bends and flexes. How does this affect penetration?’ questions Wiechers. ‘Although there might be some penetration in products like sunscreens, titanium dioxide is not a particularly toxic substance. It has been used in toothpaste for years.’ Physical activity and exposure to elements such as water and clothing can decrease the amount of absorption occurs. With regard to damaged skin, skin that has been tape-stripped has yet to show penetration while abraded skin shows some penetration.   ‘Nanotechnology has been used in sunscreens for 15 to 20 years. Although there may be some instances in which penetration occurs, the toxicity of this has yet to be determined and until a substantial amount of substantiated evidence is released, nanotechnology will continue to be present in our lives and our formulations.’