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Environment and Occupational - Human Health Risk Assessment of TiO2 and ZnO Nanoparticles Found in Sunscreen

Nanoparticles are small in size with a diameter of 100 nm (a nanometre, denoted nm, is one-billionth of a metre) or less in one or more dimensions. They exhibit several unique properties associated with their nano-size, as compared to larger particles of the same material. This is because of their high surface area-to-volume ratio, which makes the nanoparticles extremely reactive. The use of nanoparticles in sunscreens is one of the most common uses of nanotechnology in consumer products. Indeed, the global annual production of these metal oxide nanoparticles used for sunscreen products alone has been estimated to be 1000 tons in 2003-2004. TiO2 and ZnO nanoparticles used in sunscreens are in the range of 20 – 30 nm. They provide physical blocks from the harmful solar ultraviolet radiations (UV), protecting the skin from photo-damage which is known to cause skin cancers. Widespread use of these nanoparticles in sunscreens has raised concerns about their potential for causing toxic effects to humans. In addition, the nanoparticles have been released into the market without regulatory oversight. Given the extensive use of TiO2 and ZnO nanoparticles in sunscreens, it is important that the potential risks of TiO2 and ZnO nanoparticles found in sunscreens be carefully evaluated, and balanced against their UV blocking properties.

Health Risks of TiO2 and ZnO in sunscreens:
There is evidence that certain forms of TiO2 and ZnO nanoparticles can cause DNA damage in the presence of UV light via free radical formation. However, manifestation of these effects depend on the ability of TiO2 and ZnO nanoparticles to penetrate the skin and reach the viable cells of dermis. Although no conclusions can be drawn regarding absorption of these nanoparticles from damaged/diseases skin, several studies have now shown that ZnO and TiO2 nanoparticles are not absorbed through the intact skin into the bloodstream. The harmful effects of TiO2 and ZnO nanoparticles found in sunscreens may manifest in circumstances such as damaged or diseased skin where these particles are able to pass the impermeable upper layer of skin and reach viable cells.
Benefits of TiO2 and ZnO nanoparticles in sunscreens: Sunscreens provide protection against harmful effects of solar ultraviolet radiation such as skin redness (erythema), skin degeneration and skin cancer. Inorganic chemicals such as TiO2 and ZnO nanoparticles are preferred in sunscreens over existing chemical UV absorbers because of their broad-spectrum protection against both UVA (TiO2) and UVB radiation (ZnO). In addition, these TiO2 and ZnO nanoparticles are better tolerated with respect to skin irritation and sensitization as compared to the organic UV absorbers. When used in sunscreens in their larger-sized forms, ZnO and TiO2 are visible on the skin as an opaque layer, which is eliminated by utilizing the nano-scale forms of these oxides, thereby resulting in better consumer acceptance.  In addition, the UV blocking properties of these oxides are augmented when their size is reduced to nano-scale.
Taken together, current data suggests that there is minimal risk to human health from use of TiO2 and ZnO nanoparticles in sunscreens. In addition, given the broad-spectrum protection imparted by TiO2 and ZnO nanoparticles against the harmful effects of UV radiations from sun such as skin cancer, the benefits may outweigh the risks.

Risk management:  
Nanoparticles are regulated in Canada under existing legislation, including the Canadian Environmental Protection Act, the Pest Control Products Act, the Fertilizers Act, the Feeds Act, and the Food and Drugs Act. Due to the unique physical and chemical properties associated with TiO2 and ZnO nanoparticles, the potential risk of these materials remain uncertain. At present, products containing nanoparticles are used in commerce without rigorous regulatory oversight.  A two-tier risk management approach comprised of short-term and long-term components is recommended is recommended to address the potential risks of TiO2 and ZnO nanoparticles in sunscreens, as well as to ensure that information regarding sunscreens containing for TiO2 and ZnO nanoparticles is available in understandable to the public.

Short-term risk management strategies: Currently, there is no legal requirement for manufacturers to indicate the presence of nano-scale ingredients on product labels. Although there is no apparent need to avoid using sunscreen that contains nanoparticles, consumers should still be able to choose for themselves. Therefore, mandatory labeling of nanoparticles in sunscreens is recommended. In addition, active engagement with public through channels such as social media, community meetings (creating nano-groups) may serve to increase public awareness about the harmful effects of sunlight and provide useful information regarding the presence of nanoparticles in sunscreens

Long-term risk management strategies:  Long-term risk management strategies could involve toxicological research to more completely characterize the toxicological profile of TiO2 and ZnO nanoparticles used in sunscreen. In addition, further work on the development of engineered nanoparticles (ENPs) may help to ensure that ENPs are “safe by design”. Further research focused on characterizing the penetration of TiO2 and ZnO ENPSs through damaged skin would also be useful. Long-term risk management goals could involve working with international agencies to establish guidelines for the safe and effective use of nanomaterials.

Useful Links  

  1. Health Canada.
  2. OECD.
  3. US food and drug administration.
  4. Australian Government Therapeutic Good Administration.

Further reading

  1. Smijs TG, Pavel S 2011. Titanium dioxide and zinc oxide nanoparticles in sunscreens: focus on their safety and effectiveness. Nanotechnology, Science and Applications 4:95-112.
  2. FOE 2006. Friends of the Earth. Nanomaterials, sunscreens and cosmetics: Small Ingredients, Big Risks. May. Available at:
  3. Nohynek GJ, Lademann J, Ribaud C, Roberts MS 2007. Grey goo on the skin? Nanotechnology, cosmetic and sunscreen safety. Crit Rev Toxicol 37:251-277
  4. Jacobs JF, Van de Poel I, Osseweijer P 2010. Sunscreens with Titanium dioxide (TiO2) nano-particles: A societal experiment. Nanoethic 4: 03-113.    
  5. Shi H, Magaye R, Castranova, Zhao J 2013. Titanium dioxide nanoparticles: a review of current toxicological data. Particle and Fibre toxicology 10:15
  6. Nohynek GJ, Dudour EK & Roberts MS. 2008. Nanotechnology, cosmetics and the skin; is there a health risk? Skin pharmacol physiol 21:136-149.


Contributor:             Pallavi Gupta
Last reviewed:         October 31, 2016


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