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.’