Sun Care

What's The Deal with Nanoparticles in Sunscreens?

Learn more about zinc oxide and titanium dioxide nanoparticles

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It is well known that applying a generous amount of broad-spectrum sunscreen daily, even on cloudy days, is important to protect our skin.[1] Regular sunscreen use has been shown to prevent sunburns and skin cancer occurrence in several studies. [2,3] The term “broad-spectrum” refers to ingredients that protect against both ultraviolet light type A and B. Two common broad-spectrum active ingredients in sunscreen are Zinc Oxide (ZnO) and Titanium Dioxide (TiO2).[4] In traditional sunscreens, ZnO and TiO2 appeared as a cosmetically unappealing thick white paste that was difficult to blend into the skin.  

In the last decade however, the development of “nanoparticle” sunscreen formulas has led to sunscreens that appear transparent, blend more easily, and appear smoother under makeup.[5] A nanoparticle is defined as a tiny particle with a diameter less than 100 nanometers. Nanoparticles have become a hot interest in the skin care industry in many different products.[6] In 1999, the Food and Drug Administration (FDA) approved sunscreen to be formulated with nanoparticles.[4]

The use of sunscreen that is transparent and less-thick appeals to many consumers and may improve the regular use of sunscreen.[7] However, people across the world have questioned the safety of nanoparticles on both humans and on the environment.[8] In the United States, the use of nanoparticles is a regulatory problem because the FDA does not require specific labeling on nanoparticle size or quality.[9] Currently, little is known about the long-term safety of using nanoparticle sunscreen. Some of the topics of concern include: 

  1. Do nanoparticles in sunscreens create damaging reactive oxygen species (ROS)?
  2. Do nanoparticles penetrate the epidermis(the most superficial layer of skin)?
  3. Is it harmful to inhale nanoparticles?

 

ZnO and TiO2 Nanoparticles and Harmful Reactive Oxygen Species

ZnO and TiO2 are known as photocatalysts, which means that when exposed to sunlight they can create reactive oxygen species (ROS). Reactive oxygen species are harmful free-radicals that can damage cells and DNA.[10] However, it is still not clear if ZnO and TiO2 nanoparticles release free radicals that can damage the skin.  When a ray of ultraviolet (UV) light hits the ZnO or TiO2 nanoparticles, free radicals can react with proteins, lipids and DNA found in cells, potentially leading to damage.[11,12]  One study found that exposing TiO2 to light that was similar to sunlight lead to the release of ROS that lead to damage in laboratory grown skin cells.[13,14] However, this study did not look at nanoparticles of Ti02.  In another experiment using mice, ZnO nanoparticles exposed to UV type B light lead to ROS based damage in the skin.[11] It is important to note that none of these studies have been performed in human skin and we do not know if the findings would hold true. 

Additionally, the potential toxicity of these nanoparticles would only manifest if they are able to pass beyond the outermost layer of skin (epidermis) and are absorbed systemically.[15] Until we have evidence that this occurs, the risk remains theoretical. 

 

Nanoparticles Getting Into the Skin

Several studies have shown that ZnO and TiO2 nanoparticles do not penetrate beyond the stratum corneum (outermost layer) in healthy, unbroken skin.[16-20] However, in a 2016 study at the National Institute of Health (NIH), TiO2 nanoparticles were found to penetrate into the dermis surrounding the hair follicles.[21]  Studies suggest that ZnO nanoparticles also do not penetrate beyond the epidermis in human skin.[15,22,23] In fact, in one human study, volunteers applied ZnO nanoparticle sunscreen twice daily for five days.  Researchers found that only 0.01% of the Zinc got into the blood.[24] Currently, the Center for Drug Evaluation and Research of the FDA has concluded that “there is no significant penetration of TiO(2) nanoparticles through the intact normal epidermis.”[25] When used as an ultraviolet filter, the FDA has stated that ZnO, is “generally recognized as safe.”[26] The possibility that TiO¬2 may penetrate into the skin needs to be evaluated further. [21]

 

Potential Risk of Inhaling Sunscreen Nanoparticles

Toxicologists feel the greatest risk of nanoparticles is due from inhalation of zinc oxide or titanium dioxide nanoparticles.[27] According to the International Agency for Research on Carcinogens, titanium dioxide may be a carcinogen if high doses are inhaled.[28] The Environmental Working Group advises against using any spray or loose powder sunscreens that contain ZnO or TiO2 to avoid the potential toxicity from inhalation.[9] One study examined if TiO2 particles are able to distribute across biological barriers, such as the blood brain barrier (BBB).  However, this study did not prove that nanoparticles actually cross the BBB, but may alter the physiology of the BBB. It concluded that we still do not yet know the risks associated with systemic absorption.[29] 

 

Risk of Nanoparticles in Sunscreens

At this time ZnO nanoparticles in sunscreen do not appear to be dangerous when applied as a lotion to healthy skin, based on evidence that ZnO nanoparticles do not cross the epidermis.  The role of TiO2 nanoparticles is unclear as pilot studies show that they may penetrate to the dermis.  Studies in humans are missing and needed to assess if TiO2 nanoparticles release ROS in response to exposure to UV light. Inhalation of zinc oxide and titanium dioxide nanoparticles may have associated lung-based absorption. The current evidence is based on mouse studies and human studies are needed. The risk of using inhaling nanoparticles with powdered sunscreens on the face will need further study, and there needs to be more detailed work to understand if there is a safe way that these types of particles can be applied. Further research and more descriptive labeling may be important components for analyzing the safety and effectiveness of nanoparticles in sunscreen.  

At this time, both zinc oxide and titanium dioxide nanoparticles are approved for the formulation of sunscreens.  However, clinical research is limited and more long-term studies involving human skin under real sunlight exposure may help establish their safety profiles.  Both nanoparticles have potential for cell damage if they cross the epidermis, but neither have demonstrated significant skin penetration in clinical studies, although TiO2 may be able to penetrate deeper than ZnO.[21,30] It is important for ongoing research to identify risks associated with nanoparticles of ZnO and TiO2 in sunscreens. 

Sunscreens with regular zinc oxide and titanium dioxide, which are not in nanoparticle form, remain a widely available option as a broad-spectrum sunscreen. Good sun protective habits include the diligent use of sun protective clothing, avoidance of intense sunlight, and the daily use of broad-spectrum sunscreens.  

 

* This Website is for general skin beauty, wellness, and health information only. This Website is not to be used as a substitute for medical advice, diagnosis or treatment of any health condition or problem. The information provided on this Website should never be used to disregard, delay, or refuse treatment or advice from a physician or a qualified health provider.

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References

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2.    van der Pols JC, Williams GM, Pandeya N, et al. Prolonged prevention of squamous cell carcinoma of the skin by regular sunscreen use. Cancer Epidemiol Biomarkers Prev.2006;15(12):2546-2548; PMID: 17132769.

3.    Ulrich C, Jurgensen JS, Degen A, et al. Prevention of non-melanoma skin cancer in organ transplant patients by regular use of a sunscreen: a 24 months, prospective, case-control study. Br J Dermatol.2009;161 Suppl 3:78-84; PMID: 19775361.

4.    Newman MD, Stotland M, Ellis JI. The safety of nanosized particles in titanium dioxide- and zinc oxide-based sunscreens. J Am Acad Dermatol.2009;61(4):685-692; PMID: 19646780.

5.    Tran DT, Salmon R. Potential photocarcinogenic effects of nanoparticle sunscreens. Australas J Dermatol.2011;52(1):1-6; PMID: 21332685.

6.    Maynard A. Nanotechnology: a research strategy for addressing risk. Project on emerging nanotechnologies. 2006; http://www.nanotechproject.org/file_download/files/PEN3_Risk.pdf. Accessed August 22, 2016.

7.    More BD. Physical sunscreens: on the comeback trail. Indian J Dermatol Venereol Leprol.2007;73(2):80-85; PMID: 17456911.

8.    Oberdorster G, Oberdorster E, Oberdorster J. Nanotoxicology: an emerging discipline evolving from studies of ultrafine particles. Environ Health Perspect.2005;113(7):823-839; PMID: 16002369.

9.    Nanoparticles in Sunscreens. EWG 2016; http://www.ewg.org/sunscreen/report/nanoparticles-in-sunscreen/. Accessed August 22, 2016.

10.    Yang YH, Chen H, Pan G. Particle concentration effect in adsorption/desorption of Zn(II) on anatase type nano TiO2. J Environ Sci (China).2007;19(12):1442-1445; PMID: 18277647.

11.    Pal A, Alam S, Mittal S, et al. UVB irradiation-enhanced zinc oxide nanoparticles-induced DNA damage and cell death in mouse skin. Mutat Res Genet Toxicol Environ Mutagen.2016;807:15-24; PMID: 27542711.

12.    Horie M, Sugino S, Kato H, et al. Does photocatalytic activity of TiO2 nanoparticles correspond to photo-cytotoxicity? Cellular uptake of TiO2 nanoparticles is important in their photo-cytotoxicity. Toxicol Mech Methods.2016;26(4):284-294; PMID: 27142467.

13.    Dunford R, Salinaro A, Cai L, et al. Chemical oxidation and DNA damage catalysed by inorganic sunscreen ingredients. FEBS Lett.1997;418(1-2):87-90; PMID: 9414101.

14.    Arsac F, Hidaka H. DNA damage photoinduced by titanium dioxide in the presence of anionic vesicles under uv illumination: influence of sodium chloride concentration. J Oleo Sci.2007;56(11):595-601; PMID: 17938550.

15.    Cross SE, Innes B, Roberts MS, et al. Human skin penetration of sunscreen nanoparticles: in-vitro assessment of a novel micronized zinc oxide formulation. Skin Pharmacol Physiol.2007;20(3):148-154; PMID: 17230054.

16.    Tan MH, Commens CA, Burnett L, et al. A pilot study on the percutaneous absorption of microfine titanium dioxide from sunscreens. Australas J Dermatol.1996;37(4):185-187; PMID: 8961584.

17.    Lademann J, Weigmann H, Rickmeyer C, et al. Penetration of titanium dioxide microparticles in a sunscreen formulation into the horny layer and the follicular orifice. Skin Pharmacol Appl Skin Physiol.1999;12(5):247-256; PMID: 10461093.

18.    Scientific Committee on Consumer products. Opinion on Safety of Nanomaterials in Cosmetic Products. SCCP 2007. Accessed August 22, 2016.

19.    Pflucker F, Wendel V, Hohenberg H, et al. The human stratum corneum layer: an effective barrier against dermal uptake of different forms of topically applied micronised titanium dioxide. Skin Pharmacol Appl Skin Physiol.2001;14 Suppl 1:92-97; PMID: 11509913.

20.    Leite-Silva VR, Sanchez WY, Studier H, et al. Human skin penetration and local effects of topical nano zinc oxide after occlusion and barrier impairment. Eur J Pharm Biopharm.2016;104:140-147; PMID: 27131753.

21.    Coelho SG, Patri AK, Wokovich AM, et al. Repetitive Application of Sunscreen Containing Titanium Dioxide Nanoparticles on Human Skin. JAMA Dermatol.2016;152(4):470-472; PMID: 26913928.

22.    Dussert AS, Gooris E, Hemmerle J. Characterization of the mineral content of a physical sunscreen emulsion and its distribution onto human stratum corneum. Int J Cosmet Sci.1997;19(3):119-129; PMID: 18507639.

23.    Zvyagin AV, Zhao X, Gierden A, et al. Imaging of zinc oxide nanoparticle penetration in human skin in vitro and in vivo. J Biomed Opt.2008;13(6):064031; PMID: 19123677.

24.    Gulson B, McCall M, Korsch M, et al. Small amounts of zinc from zinc oxide particles in sunscreens applied outdoors are absorbed through human skin. Toxicol Sci.2010;118(1):140-149; PMID: 20705894.

25.    Sadrieh N, Wokovich AM, Gopee NV, et al. Lack of significant dermal penetration of titanium dioxide from sunscreen formulations containing nano- and submicron-size TiO2 particles. Toxicol Sci.2010;115(1):156-166; PMID: 20156837.

26.    Smijs TG, Pavel S. Titanium dioxide and zinc oxide nanoparticles in sunscreens: focus on their safety and effectiveness. Nanotechnol Sci Appl.2011;4:95-112; PMID: 24198489.

27.    Borm PJ, Kreyling W. Toxicological hazards of inhaled nanoparticles--potential implications for drug delivery. J Nanosci Nanotechnol.2004;4(5):521-531; PMID: 15503438.

28.    Warheit DB, Webb TR, Sayes CM, et al. Pulmonary instillation studies with nanoscale TiO2 rods and dots in rats: toxicity is not dependent upon particle size and surface area. Toxicol Sci.2006;91(1):227-236; PMID: 16495353.

29.    Disdier C, Devoy J, Cosnefroy A, et al. Tissue biodistribution of intravenously administrated titanium dioxide nanoparticles revealed blood-brain barrier clearance and brain inflammation in rat. Part Fibre Toxicol.2015;12:27; PMID: 26337446.

30.    O'Keefe SJ, Feltis BN, Piva TJ, et al. ZnO nanoparticles and organic chemical UV-filters are equally well tolerated by human immune cells. Nanotoxicology.2016;10.1080/17435390.2016.1206148:1-10; PMID: 27345703.