Nano Sunscreen

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Most of the sun’s radiation is UV, Vis & IR :

Source: Adapted from http://www.ucar.edu/learn/imgcat.htm

Slide 10

What is Radiation?

Light radiation is often thought of as a wave with a wavelength (l) 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

Slide 11

Two Ways to Think about Radiation Energy

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

Slide 12

Two Ways to Think about Radiation Energy

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)

Source: 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 for many locations in the US daily: http://www.epa.gov/sunwise/uvindex.html

Slide 13

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)

High Energy Low Energy

Source: http://www.arpansa.gov.au/is_sunys.htm

As far as we know, visible and IR radiation don’t harm the skin

Slide 14

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 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.

Skin Damage II

Slide 15

Sun Radiation Summary

Increasing

Energy

Increasing

Wavelength

Slide 16