hen putting on sunscreen, you are spreading on a chemical that absorbs in the ultraviolet region of the electromagnetic spectrum.  Ultraviolet radiation can be very harmful to the skin, by damaging genetic material near the skin’s surface.  Because molecules can act as filters, the right molecules can filter out the harmful radiation from the sun, and that is how sunscreen works. 

          Sunscreen and your body’s natural defense to UV light contain molecules that strongly absorb in the UV region. The compound melanin is produced in skin cells and absorbs strongly in the UV region. Melanin pigments your skin, resulting in darker skin after extended exposure to sunlight. Sunscreen producers produce their products with a Sun Protection Factor (SPF).  

Sun Protection Factor measures the protection provided by sunscreen by giving a ratio of the time it would take for skin to be in the sun and maintain a low risk for sun burn.  The SPF (ranging from 0 to 60+) measures protection against UVB but does not take UVA into account. Some sunscreens protect against UVA rays, but they have no SPF rating.  To figure out which SPF you should use, take the time it would take you to burn without sunscreen and multiply that number by the SPF factor of the product you are using. Dividing by a 1 hour of 60 minutes, you will get the amount of hours you will have with protection from sunburn.  

          Sunscreen helps protect against short-term effects such as sunburn. By preventing acute and/or recurring sunburns, sunscreen also provides protection against the long-term effects of the sun (skin cancer, premature aging, etc). The chemical composition of sunscreen determines the range of wavelengths it protects against. Some common compounds include: avobenzone (Parsol®1789) which protects against UVA rays, oxybenzone, octrocrylene which protects against UVB and some UVA rays, and homosalate, octisalate protecting against UVB rays. 

Our project tested UVA and UVB radiation. UVA radiation ranges from 320-400 nanometers (nm) and UVB radiation ranges from 290-320 nanometers (nm). UVA radiation has the lowest energy of the UV wavelengths falling just above the visible range. It causes tanning, but long term exposure leads to premature aging and may cause damage that contributes to other conditions, due to deep penetration into the skin. UVB radiation is of shorter wavelength and higher energy than UVA. This kind of radiation is responsible for sunburns (long-term exposure is linked with skin cancer).