Saving Your Students’ Skin. Undergraduate Experiments That Probe UV Protection by Sunscreens and Sunglasses

In recent years, exposure to ultraviolet (UV) radiation has been linked to a number of human health problems, including sunburn, skin cancer, premature aging of the skin, cataracts, and immune suppression (1–3). At the same time, evidence of aerosol-induced damage to the earth’s primary UV filter, the ozone layer, has increased (4 ), and skin cancer rates have risen to more than 900,000 cases per year (5 ), further intensifying concern over exposure to UV radiation. UV radiation penetrates the ozone layer over two wavelength regimes, UVB (290–320 nm) and UVA (320–400 nm). UVB acts directly on biological molecules, causing skin cancer, skin aging, and the familiar delayed sunburn that arises 12–24 hours after exposure (1, 6, 7 ). In contrast, UVA acts indirectly through reactive oxygen species, causing an “immediate” sunburn that diminishes within 2 hours after exposure, and potentially plays a role in skin cancer and delayed sunburn (6, 7 ). Concern over such adverse health effects has led to the development of sunscreens and sunglasses, which provide the skin and eyes with UV protection. Sunscreens and sunglasses protect primarily by absorbing UV radiation, dissipating the absorbed energy as heat before it can damage photosensitive biological molecules (8, 9). In addition, sunscreens and sunglasses may provide extra protection by reflecting or scattering UV radiation (8, 9). A sun protection factor (SPF) for rating the UVB (i.e., delayed sunburn) protection provided by sunscreens was developed in the 1970s by Plough (10) and was recently codified by the Food and Drug Administration (11). The SPF is defined by the ratio (9, 11)