Copyright © 2005 SRI International Nano Sunscreen The Wave of the Future? Modified slightly from the NanoSense web materials 2 Nano Products • Number of products using nanomaterials is growing very rapidly – Doubling every year? • Clothing, food and beverages, sporting goods, coatings, cosmetics, personal care • Sunscreens: many use nanomaterials – Some labeled as containing nanoparticles – Some not labeled 3 http://www.masspolicy.org/ pdf/workshop/rejeski.pdf 4 Why Use Sunscreen? Too much unprotected sun exposure leads to: • Premature skin aging (e.g. wrinkles) • Sunburns • Skin cancer Sources: http://www.oasishospital.org/previousnews.html; http://wohba.com/archive/2005_03_01_archive.html 5 Skin Cancer Rates are Rising Fast Skin cancer: • Is ~50% of all cancer cases • Has > 1 million cases diagnosed each year • Causes 1 person to die every hour Probability of getting skin cancer: 1930 : 1 in 5,000 2004 : 1 in 65 2050 : 1 in 10… http://www.skincarephysicians.com/skincancernet/whatis.html; http://www.msu.edu/~aslocum/sun/skincancer.htm Causes of the increase: • Decrease ozone protection • Increased time in the sun • Increased use of tanning beds Sources: http://www.msnbc.msn.com/id/8379291/site/newsweek/ ; 6 What are sun rays? • The sun emits several kinds of electromagnetic radiation: Visible (Vis), Infrared (IR) and Ultra Violet (UV) • Each kind is distinguished by a characteristic wavelength, frequency and energy • Higher energy radiation can damage our skin Source: http://www.arpansa.gov.au/is_sunys.htm High Energy Low Energy 7 8 The Full Electromagnetic Spectrum • Visible, Infrared and UV radiation are only part of the full spectrum of electromagnetic radiation Source: http://www.mhhe.com/physsci/astronomy/arny/instructor/graphics/ch03/0305.html 9 The Sun’s Radiation Spectrum • ~ 43% is in the visible range • ~ 49% is in the near infrared range • ~ 7% is in the ultraviolet range • < 1% is x-rays, gamma waves, and radio waves . Most of the sun’s radiation is UV, Vis & IR : Source: Adapted from http://www.ucar.edu/learn/imgcat.htm 10 What is Radiation? • Light radiation is often thought of as a wave with a wavelength (λ) and frequency (f) related by this equation: Source: http://www.pueblo.gsa.gov/cic_text/health/sun_uv/sun-uv-you.htm • Since c (the speed of light) is constant, the wavelength and frequency are inversely related • This means that light with a short wavelength will have a high frequency and visa versa [...]... energy is in each packet but also to the total number of packets arriving at a given location (such as our skin) • Total Energy depends on many factors including the intensity of sunlight • The UV Index rates the total intensity of UV light for many locations in the US daily: http:// www.epa.gov/sunwise/uvindex.html Source: http://www.epa.gov/sunwise/uvwhat.html 13 Skin Damage • The kind of skin damage is. .. Ways to Think about Radiation Energy 1 Energy Comes in Packets (Photons) • The size of an energy packet (E) is determined by the frequency of the radiation (f) • • Radiation with a higher frequency has more energy in each packet The amount of energy in a packet determines how it interacts with our skin E E∝f f 12 Two Ways to Think about Radiation Energy 2 Total Energy • This relates not only to how... by the size of the energy packet ( E = h x f) • The UV spectrum is broken into three parts: – Very High Energy (UVC) – High Energy (UVB) – Low Energy (UVA) • As far as we know, visible and IR radiation don’t harm the skin Source: http://www.arpansa.gov.au /is_ sunys.htm High Energy Low Energy 14 Skin Damage II • Very high energy radiation (UVC) is currently blocked by the ozone layer (ozone hole issue)... What are the most important factors to consider in choosing a sunscreen? 2 How do you know if a sunscreen has “nano” ingredients? 3 How do “nano” sunscreen ingredients differ from other ingredients currently used in sunscreens? A Brief History of Sunscreens: The Beginning • First developed for soldiers in WWII (1940s) to block “sunburn causing rays” These were called UVB rays WWII soldier in the sun... radiation (UVB) does the most immediate damage (sunburns) • But lower energy radiation (UVA) can penetrate deeper into the skin, leading to long term damage Source: N.A Shaath The Chemistry of Sunscreens In: Lowe NJ, Shaath NA, Pathak MA, editors Sunscreens, development, evaluation, and regulatory aspects New York: Marcel Dekker; 1997 p 263-283 15 Sun Radiation Summary Radiation Type Characteristic Wavelength... ingredients different from organic ones? How might this affect the way they absorb UV light? 29 Inorganic Ingredients: The Basics • Atoms Involved – Zinc or Titanium – Oxygen • Structure – Ionic attraction – Cluster of ions – Formula unit doesn’t dictate size • Size – Varies with # of ions in cluster – ~10 nm – 300 nm Detail of the ions in one cluster Group of TiO2 particles Source: http://www.microspheres-nanospheres.com/Images/Titania/TIO2%20P7.jpg... how this looks, so they don’t use sunscreen with inorganic ingredients • Of the people who do use them, most apply too little to get full protection Source: http://www.4girls.gov/body/sunscreen.jpg 34 Why Do They Appear White? • Traditional ZnO and TiO2 clusters are large – (> 200nm) • Large clusters scatter visible light – (400-700 nm) – Maximum scattering occurs for wavelengths twice as large as the. .. http://www.bbc.co.uk/wiltshire/content/articles/2005/05/05/peoples_war_feature.shtml http://www.arpansa.gov.au /is_ sunys.htm 19 A Brief History of Sunscreens: The SPF Rating • Sunscreens first developed to prevent sunburn – Ingredients were good UVB blockers • SPF (Sunscreen Protection Factor) Number – Measures the strength of UVB protection only – Higher SPF # = more protection from UVB – Doesn’t tell you anything about... Different number of ions can cluster together – Must be a multiple of the formula unit • ZnO always has equal numbers of Zn and O atoms • TiO2 always has twice as many O as Ti atoms ~100 nm TiO2 particle Source: Images adapted from http://www.cse.clrc.ac.uk/msi/projects/ropa.shtml ~200 nm TiO2 particle 31 Inorganic Ingredients: UV Absorption • Inorganics have a different absorption mechanism than organics... http://www.shop.beautysurg.com/ProductImages/skincare/14520.jpg 20 A Brief History of Sunscreens: The UVA Problem • UVA rays have no immediate visible effects but cause serious long term damage – Cancer – Skin aging • Sunscreen makers working to find UVA blockers – No official rating of UVA protection yet Source: http://www.cs.wright.edu/~agoshtas/fig8.jpg Twenty different skin cancer lesions 21 22 How do you know if your sunscreen is a good UVA blocker? . http://www.epa.gov/sunwise/uvwhat.html • Total Energy depends on many factors including the intensity of sunlight • The UV Index rates the total intensity of UV light. skin 12 Two Ways to Think about Radiation Energy 2. Total Energy • This relates not only to how much energy is in each packet but also to the total number of packets