Figure 1. Nanoparticles are now used in the vast majority of sunscreen products on the market, as well as many other cosmetic products. Image Credits: Photos.com.
Nanoparticles and other nanostructured materials have unique properties which cannot be achieved when working with the bulk form of the material. Applications for these special properties have been suggested in many industries - the cosmetics industry is one of those most eager to make the most of the opportunities presented by nanotechnology.
Nanomaterials have been used to try and improve the performance of a wide range of products, from moisturiser and anti-ageing creams to hair care. Most of the main cosmetics manufacturers have at least some "nano-enhanced" products in their range. However, there is still some controversy over the safety of these novel materials, and the regulation of nanomaterials in cosmetics is lax or unclear in many parts of the world.
Benefits of Nanomaterials in Cosmetics
The two main uses for nanoparticles in cosmetic products are UV filtering and delivery of active ingredients.
Titanium dioxide and zinc oxide are both used extensively in sunscreens to prevent UV damage to the skin - the nanoformulations of these materials have been shown repeatedly to give much better performance than larger particles, reflecting visible light and absorbing UV with very high efficiency.
A wide range of nanostructures have been proposed as delivery mechanisms for cosmetic ingredients in moisturisers, anti-ageing creams, and other skincare products - from lipid nanoparticles to dendritic or hyperbranched polymers. Again, these nanostructured materials show much more efficient delivery of the active ingredient to the skin cells.
Lipid nanoparticles are particularly effective, as they can merge with the lipid bilayer in cell membranes, facilitating the delivery of compounds which would otherwise not be able to enter the cell.
Lipid nanostructures, and dendritic biopolymers, provide the additional benefit of being totally non-toxic and biocompatible. This is in contrast to the metal and metal oxide nanoparticles - there are still doubts about their safety for dermal use.
Health Concerns over Nanoparticles in Cosmetics
The size-dependent properties which enable nanomaterials to perform so much better than their bulk counterparts can also potentially create negative effects - their novel physical and chemical properties may alter the toxicity of the materials in ways we do not yet fully understand. This has limited the adoption of nanomaterials in many industry sectors, despite their enhanced performance - this is a particularly crucial issue in cosmetics, as the products are designed to be applied directly to human skin.
In July 2012, materials supplier Antaria came under fire from environmental groups for providing metal oxide powders containing nanoparticles for a number of sunscreen brands which were advertised as nanoparticle-free. This highlights the issue with classification of nano-enhanced products - the particle size distribution of many powders will include some nanoscale particles, and it is not clear how much this affects the health implications of nanomaterials.
Nanoparticle-containing sunscreens have come under scrutiny recently. Although research on the topic is still limited, some initial results indicate that the UV-absorbing properties of TiO2 and ZnO2 could also catalyse the production of free radicals, which could potentially lead to increased risk of cell damage and skin cancer. This makes quantifying this effect very difficult, as skin cancer can also be caused by UV damage, which the nanoparticles protect against.
Some studies have also shown metal oxide nanoparticles passing through the skin into the bloodstream - the effects of long-term exposure to nanoparticles in the bloodstream has not yet been conclusively determined.
Whether nano-enhanced sunscreens and other cosmetics turn out to pose a significant health risk or not, the negative publicity given to nanotechnology as a result of this issue are likely to affect consumer acceptance of nanomaterials well into the future, even when their effects are better understood - not just in cosmetics, but in many other industries as well.
Regulatory and legislative bodies around the world are beginning to introduce clearer rules about nanotechnology. This is a very difficult task, however, when the research is complicated and incomplete, as it is for nanotoxicology. Lots more work is underway to better understand the longer-term impact of nanomaterials on human health.
In the meantime, cosmetics manufacturers are developing more and more nanoformulated products. Nanoemulsions and nanocrystals are becoming more and more popular in skincare products, and they are usually made of organic materials with very few toxicological issues.
Whatever the outcome of the current controversies, it seems highly likely that nanomaterials will feature heavily in the future of the cosmetic industry.