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Sunscreen UV Ultraviolet Light and SPF. UVA (ultraviolet-A)  Long wave solar rays of 320-400 nanometer (billionths of a meter).  Although less likely.

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Presentation on theme: "Sunscreen UV Ultraviolet Light and SPF. UVA (ultraviolet-A)  Long wave solar rays of 320-400 nanometer (billionths of a meter).  Although less likely."— Presentation transcript:

1 Sunscreen UV Ultraviolet Light and SPF


3 UVA (ultraviolet-A)  Long wave solar rays of 320-400 nanometer (billionths of a meter).  Although less likely than UVB to cause sunburn, UVA penetrates the skin more deeply, and is considered the chief culprit behind wrinkling, leathering, and other aspects of "photoaging."  The latest studies show that UVA not only increases UVB 's cancer-causing effects, but may directly cause some skin cancers, including melanomas.

4 UVB (ultraviolet-B)  Short-wave solar rays of 290-320 nanometers.  More potent than UVA in producing sunburn, these rays are considered the main cause of basal and squamous cell carcinomas as well as a significant cause of melanoma.

5 UVC (Ultraviolet-C)  Short-wave solar rays of 200-290 nanometers.  Completely absorbed by gases in the atmosphere before it reaches the ground.  The shorter the wavelength, the greater the energy level of light and the more damage it can do.

6 SPF- Sun Protection Factor  The effectiveness of sunscreen is indicated by the sun protection factor.  measures the length of time a product protects against skin reddening from UVB, compared to how long the skin takes to redden without protection.  If it takes 20 minutes without protection to begin reddening, using an SPF 15 sunscreen theoretically prevents reddening 15 times longer -- about 5 hours. (Actually, it may take up to 24 hours after sun exposure for redness to become visible.) To maintain the SPF, reapply sunscreen every two hours and right after swimming.

7 Sunscreens and sun blocks  Sunscreens chemically absorb UV rays, sunblocks physically deflect them.  Sunscreen has long blocked UVB effectively, but until recently provided less UVA protection.  New ingredients such as octylcrylene and the benzophenones have improved sunscreen's defenses against shorter UVA rays, and the revolutionary chemical avobenzone (Parsol 1789) works against all UVA wavelengths.

8 Active Ingredients  Oxybenzone is a chemical used in sunscreen to block UVB. It is a derivative of Benzophenone. It is also known as 2-Hydroxy-4-methoxybenzophenone, [2-Hydroxy-4-methoxyphenyl]phenylmethanone and Benzophenone-3.sunscreenUVBBenzophenone

9 Avobenzone  4-t-butyl-4'-methoxy-dibenzoylmethane  C 20 H 22 O 3  protects against long wavelength UVA rays.  These active ingredients are photon absorbing agents and they function by absorbing UV radiation.

10  Once the UV radiation has been absorbed, they undergo very rapid vibrational relaxation back to the ground state.  Once in the ground state, these molecules can absorb another photon to repeat the process.

11 Titanium Oxide  Titanium dioxide (TiO 2 ) does not absorb UV light at all, but rather blocks light from reaching your skin by reflecting or scattering it.  It is sometimes referred to as a “nonchemical” sunblock (as a chemistry student, you should find this silly because, of course, it’s a chemical). TiO 2 is different, however, from the organic compounds because the skin does not absorb it and it works by physically blocking the light.

12  TiO 2 sunscreens are extremely effective and hypoallergenic.  Another consumer product also uses TiO 2 —white paint! TiO 2 sunblocks were not widely used in the past because they stayed white when applied.  The particle size of new “micronized” TiO 2 formulations is so small that TiO 2 sunblock is invisible on skin.

13 The photochemistry of Sunscreen  To understand how sunscreens work, we need to understand what happens when molecules interact with light energy.  In general, when a molecule absorbs a photon whose energy is high enough, an electron is promoted from a lower energy level to a higher one. The molecule is said to go from its ground state to an excited state.  Once in the excited state the molecule has several different pathways that it can take: The molecule can emit a photon and return to its ground state.

14  The molecule can return to its ground state by emitting the energy thermally through a series of vibrational transitions.  The molecule can undergo some type of reaction from the excited state, which is generally termed photochemistry.  Finally, the molecule can convert to a lower energy state.  The favored path will be the one which is most rapid.

15 Natural protection- Melanin  Humans’ natural protection mechanism against sunlight’s (UV) damaging effect involves specialized cells called melanocytes.  When the skin is irritated by exposure to UV light, these specialized cells produce a black pigment called melanin and distribute it through the skin.  The presence of melanin results in a tanned looked.

16  Melanin protects the skin by absorbing the UV radiation thus preventing the type of photochemical reactions that produce skin damage.

17 References   benzone.html benzone.html 

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