With each passing hour in the sun, each person is exposed to and suffers damage from ultraviolet (UV) radiation. UV radiation, which comes in three wavelengths (UVA, UVB, and UVC), is all harmful to humans and may cause skin damage, and in the worst case scenario, could cause skin cancer such as melanoma. Using sunscreen is a way to protect oneself from these damaging rays, this experiment is designed to test what the minimum SPF (sun protection factor) is for ideal sun protection from UVA and UVB light rays. The best SPF is one that protects not only against UVA rays (the weaker of the two), but also protects from the more detrimental UVB rays. Yeast is a fungus, but is made up of eukaryotic cells. This is why I chose it as a sample specimen to compare to humans; in general, the damage from UV radiation that affects yeast can be used as a model for human skin cells. A UV sensitive type of yeast that lacks an enzyme necessary for DNA repair (therefore, cannot heal ultraviolet damage), I exposed it to both UVA and UVB lighting with various SPF sunscreens to observe the number of dead yeast. Regular baker's yeast was used as a control to compare to the UV sensitive yeast. Each UV sensitive plate had sunscreen with an SPF of either 15, 30, 50, 50 sport, or 90. After the exposure to UV radiation, the plates were observed under a microscope to estimate living and dead yeast counts. With these results, I can a direct relationship between the SPF levels and numbers of dead yeast, and these results are prominent in the UVB cultures I made. The yeast exposed to UVB light died at a more rapid rate than the ones exposed to UVA light, therefore, a higher SPF is needed to protect the yeast against UVB radiation. Due to a certain contamination in my cultures, however, I was forced to re-make some of the UVA experiments. Although this experiment is relatively small in terms of what I meant to accomplish, I believe I had a solid idea and approached it with an open mind and a keenness to learn. I learned about UVB doing more damage than UVA light, which supports the finding that it is required to have an SPF of 50 or higher (preferably SPF 50 sport) to be safe from most UV radiation. This experiment shows just how important it is to wear sunscreen to protect skin from both kinds of harmful radiation, and also demonstrates that UVB, in fact, does have a more negative impact on human skin than UVA radiation.