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					Nano Sunscreen
The Wave of the Future?

Modified slightly from the NanoSense web materials

Copyright © 2005 SRI International


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 df/workshop/rejeski.pdf


Why Use Sunscreen?
Too much unprotected sun exposure leads to: • • • Premature skin aging (e.g. wrinkles) Sunburns Skin cancer



Skin Cancer Rates are Rising Fast
Probability of getting skin cancer: 1930 : 1 in 5,000 2004 : 1 in 65 2050 : 1 in 10… Skin cancer: • Is ~50% of all cancer cases • Has > 1 million cases diagnosed each year • Causes 1 person to die every hour

Causes of the increase: • Decrease ozone protection • Increased time in the sun • Increased use of tanning beds
Sources: ;;


What are sun rays?
• The sun emits several kinds of electromagnetic radiation: Visible (Vis), Infrared (IR) and Ultra Violet (UV)

High Energy

Low Energy

• Each kind is distinguished by a characteristic wavelength, frequency and energy • Higher energy radiation can damage our skin



The Full Electromagnetic Spectrum
• Visible, Infrared and UV radiation are only part of the full spectrum of electromagnetic radiation



The Sun’s Radiation Spectrum
Most of the sun’s radiation is UV, Vis & IR :

• ~ 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

Source: Adapted from


What is Radiation?
• Light radiation is often thought of as a wave with a wavelength (l) and frequency (f) related by this equation:

• 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


Two 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





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 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:



Skin Damage
• The kind of skin damage is determined 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

High Energy

Low Energy



Skin Damage II
• Very high energy radiation (UVC) is currently blocked by the ozone layer (ozone hole issue) • High energy radiation (UVB) does the most immediate damage (sunburns) • But lower energy radiation (UVA) can penetrate deeper into the skin, leading to long term Source: N.A. Shaath. The Chemistry of Sunscreens. In: Lowe NJ, Shaath NA, Pathak MA, editors. Sunscreens, development, damage evaluation, and regulatory aspects. New York: Marcel Dekker; 1997. p. 263-283.


Sun Radiation Summary
Radiation Type Characteristic Wavelength (l) Energy per Photon % of Total Radiation Reaching Earth ~0% (<1% of all UV) Effects on Human Skin Visible to Human Eye? No


~200-290 nm (Short-wave UV)

Increasing Energy

DNA Damage

High Energy Medium Energy


~290-320 nm (Mid-range UV)
~320-400 nm (Long-wave UV)

~.35% (5% of all UV)

Sunburn DNA Damage Skin Cancer
Tanning Skin Aging DNA Damage Skin Cancer None Currently Known




Low Energy

(95 % of all UV) ~43 %


~400-700 nm

Lower Energy



~700-120,000 nm
Increasing Wavelength

Lowest Energy


Heat Sensation (high l IR)



With all of this possible damage, it pays to wear sunscreen, but which one should you use?



Which Sunscreen Should You Use???

New and Improved Now with Nano-Z Broadband Protection Safe for Children SPF 50 Goes on Clear


The Challenge: 3 Essential Questions
1. 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

Shorter wavelengths (more energy) called UVC

Longer wavelengths (less energy) called UVA



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 protection from UVA
Sources: and


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

Twenty different skin cancer lesions


How do you know if your sunscreen is a good UVA blocker?


Know Your Sunscreen: Look at the Ingredients
• UV blocking agents suspended in a lotion – “Colloidal suspension”

• Lotion has “inactive ingredients” – Don’t block UV light • UV blocking agents are “active ingredients” – Usually have more than one kind present • Two kinds of active ingredients – Organic ingredients and inorganic ingredients
Source: Original Image


Organic Ingredients: The Basics
• Organic = Carbon Atoms – Hydrogen, oxygen & nitrogen atoms are also often involved • Structure – Covalent bonds – Exist as individual molecules • Size – Molecular formula determines size – Typical a few to several dozen Å (<10 nm)
Sources: and original image

Octyl methoxycinnamate (C18H26O3) an organic sunscreen ingredient


Organic Ingredients: UV Absorption
1. Electrons capture the energy from UV rays 2. They jump to higher energy levels hf=2.48 eV 3. The energy is released as infrared rays which are harmless (each ray is low in energy)

3hf=2.48 eV

Source: Adapted from


Organic Ingredients: Absorption Range
• Organic molecules only absorb UV rays whose energy matches difference between electron energy levels – Different kinds of molecules have different peaks and ranges of absorption – Using more than one kind of ingredient (molecule) gives broader protection

One Ingredient

Two Ingredients

Three Ingredients

Source: Graphs adapted from


Organic Ingredients: Absorption Range cont.
• Most organic ingredients that are currently used were selected because they are good UVB absorbers – The FDA has approved 15 organic ingredients • Sunscreen makers are trying to develop organic ingredients that are good UVA blockers – Avobenzone (also known as Parasol 1789) is a new FDA approved UVA blocker



How are inorganic sunscreen ingredients different from organic ones?
How might this affect the way they absorb UV light?


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: and image adapted from


Inorganic Ingredients: Cluster Size
• Inorganic ingredients come in different cluster sizes (sometimes called “particles”) – 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

~200 nm TiO2 particle


Inorganic Ingredients: UV Absorption
• Inorganics have a different absorption mechanism than organics • Absorb consistently through whole UV range up to ~380nm • How is the absorption pattern different than for organics?
Source: Graph adapted from


If inorganic sunscreen ingredients block UVA light, why doesn’t everybody use them?



Appearance Matters
• Traditional inorganic sunscreens have appear white on our skin

• Many people don’t like 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


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 clusters • The scattered light is reflected to our eyes, appearing white
Source: Original image


Why don’t organic sunscreen ingredients scatter visible light?

Source: Adapted from


Organic Sunscreen Molecules are Too Small to Scatter Light

~200 nm TiO2 particle


(Note that these images are not drawn to scale)
Source: Images adapted from and


Waves and obstacles
• Waves go around small obstacles • Waves scatter all around from obstacles of sizes comparable to a wavelength • Water wave (ripple tank) simulation:


What could we do to inorganic clusters to prevent them from scattering visible light?

Source: Adapted from


Nanosized Inorganic Clusters
• Maximum scattering occurs for wavelengths twice as large as the clusters – Make the clusters smaller (100 nm or less) and they won’t scatter visible light

Source: Graph adapted from


Nano-Sunscreen Appears Clear
Nanosized ZnO particles Large ZnO particles



Let’s Look at Some Real Data…
• Three sunscreens were tested for scattering with different wavelengths of light – One contains nanosized inorganic ingredients – One contains traditional inorganic ingredients – One contains organic ingredients Can you answer these three questions: 1. Which one is which and how do you know? 2. Will each one appear white or clear on your skin? 3. What size (approximately) are the clusters in each sunscreen?



Light Scattering by Three Sunscreens
Sunscreen 1
100 90

Sunscreen 2

Sunscreen 3

Percent of Light Scattered

80 70 60 50 40 30 20 10 0 300 310 320 330 340 350 360 370 380 390 400 410 420 430 440 450 460 470 480 490 500

Wavelength of Light


In Summary…
• Nanoparticle sunscreen ingredients are small inorganic clusters that: – Provide good UV protection by absorbing both UVB and UVA light – Appear clear on our skin because they are too small to scatter visible light



Essential Questions: Time for Answers
1. 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?

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