At ski areas, average UV was moderate to low during the winter season, though large variation occurred. Adults at ski areas were intermittently exposed to levels of UV warranting precautions against skin exposure. UV was dangerously high on many late winter and early spring days when UV readings up to 10 were observed. This study found that substantial UV radiation occurred from two other sources: diffuse atmospheric radiation and reflected radiation from the snowy surface. The short wavelength of UV causes dispersion resulting in substantial diffuse UV in the atmosphere and considerable UV is reflected off snowy surfaces.
These three sources produce a multidirectional barrage of UV that explains ski patrollers’ anecdotal accounts of sunburning in their nostrils and underscores the need for comprehensive sun protection. Outdoor enthusiasts should stay in shade and wear brimmed hats but these practices may be insufficient to fully protect individuals in high altitude, outdoor, snow-covered winter environments where UV is diffuse and reflected not just direct. Shade and hats should be supplemented with broad-spectrum high SPF sunscreen, sunglasses, and clothing that protect skin surfaces from diffuse and reflected UV radiation in addition to direct solar UV radiation.
People cannot directly detect UV when deciding to take precautions. Instead, they must infer UV levels from its link to temporal, geographic, and meteorological characteristics or rely on UV Index forecasts. As expected, proximity to noon, deviation from the winter solstice, lower latitudes.higher altitudes, and less cloud cover were associated with increased UV. Proximity to noon, deviation from winter solstice, and cloud cover have the most pronounced affect on UV levels at ski areas. The association of temperature with UV may be spurious, produced by increasing infrared radiation toward noon and in early spring when UV also increases.
Skiers and snowboarders evidently monitor outdoor alpine environments in two ways, for sun protection and cold protection. For sun protection, they rely mainly on clear skies as a UV cue. They correctly link clear skies with the need for UV protection and use and reapply more sunscreen since more UV is present on clear days. However, extensive diffuse and reflected UV occurs on cloudy days at midday in the spring, and cloud cover can change within hours. Males pay more attention to seasonality when taking precautions while women pay more attention to time of day. Routine use of moisturizers and make-up with sunscreen may account in part for women’s consistent sunscreen use across season. Lighter-skinned individuals appear to base sun protection decisions correctly on latitude but do not adjust for altitude.
A second judgment made by outdoor enthusiasts regards how much clothing to wear to maintain body heat and avoid frostbite. On cloudy days, when the weather is more inclement, skiers and snowboarders are more likely to wear head covering and cover their ears, neck, and face. Ironically these excellent sun safety behaviors are more likely on cloudy days when UV is a bit lower and less likely to be worn on sunny days when UV is higher. Older adults rely less on temperature than younger adults, suggesting they learned not to trust this unreliable UV cue. Sun safety promotions should remind skiers and snowboarders to wear sun protective clothing on sunny days as well. In warm weather changing to lighter-weight headwear and clothing could help manage overheating, on warm, sunny days and still obtain protection.
Unfortunately, little association exists between any sun protection behavior and time of day or season. Skiers and snowboarders appear to ignore both the fact that UV increases as spring approaches and is higher near solar noon each day. While cloud cover does depress the amount of UV reaching the ski area, this reduction, perhaps by as much as 50%, does not eliminate all UV in late winter and early spring and at midday when UV is high. Individuals should be cautious about cloud cover as a UV indicator and need to consider season and time of day the most reliable indicators of UV. One good sign is that sunscreen reapplication was more likely nearer to noon. Unfortunately it appears that warm temperatures, a very unreliable cue to UV levels, continue to be considered in adults’ sun protection decisions during winter and spring outdoor recreation just as it is in the summer.32
People are both accurate and inaccurate in their UV assessments. People wear sunscreen, lip balm, and headgear with brims based on inferences about UV – using them more frequently on clear days and at lower latitudes. Sunscreen was reapplied when UV was judged to be high. However, protective clothing decisions appear to be motivated by inclement weather concerns rather than elevated UV. Probably people also apply sunscreen more than 30 minutes prior to skiing or snowboarding due to inclement weather rather than due to advice that sunscreen is most effective when applied beforegoing outdoors. They may feel it is more difficult or uncomfortable to apply sunscreen in inclement weather so they do so before arriving on the mountain. Skiers and snowboarders should be encouraged to pre-apply sunscreen on sunny and cloudy days since sunscreen compounds need time to be absorbed by the skin to be effective.33,34,35
Outdoor recreation venues should consider publishing UV forecasts to help guests make informed sun safety decisions. However, UV forecasts do not always promote increased sun safety12
as individuals continue to rely on “rules of thumb” like associating high UV with clear.not cloudy days, and warm, not cold days, regardless of season or time of day.
It was surprising that UV was less strongly related to latitude and altitude than other variables. This finding may be due to restricted range of latitudes (all but one ski area was between 34° N and 50° N) and high base altitudes (all but one were in high altitude mountain locations), Despite these findings, outdoor recreators should still take into account latitude and altitude when judging UV as prior research shows that UV is elevated at low latitudes and high elevation, and when combined may result in UV levels in winter that can burn and damage the skin.
This study was limited to ski areas in Western North America. It would be valuable to examine if outdoor recreation enthusiasts in countries with more sun safety promotion rely on different environmental cues to UV when making sun protection decisions. Our data are also limited to outdoor recreation during the winter and early spring period and not applicable to summer when UV is high and temperatures are much warmer.
During outdoor recreation in winter and spring people in alpine environments are bathed in UV. Fortunately, they take some precautions when UV is high, but their sun protection is associated with clear skies and temperature, not more reliable temporal cues, season or proximity to noon, and geographic cues, altitude and latitude. More sophisticated sun safety promotions are needed that both teach people to take precautions and to judge accurately when UV is high.