Skiers, beware: you’re exposed to more ultraviolet radiation than you think. Hot chocolate at midday — preferably somewhere shady — may be a good idea.

Scientists studying sun safety took multiple readings of ultraviolet radiation at 32 high-altitude ski areas in western North America and interviewed thousands of skiers to find out whether they took precautions against the sun, like wearing hats, sunscreen and goggles, at appropriate times. Their conclusion was: only occasionally.

“There were lots of findings, but the big takeaway is that people do not know when UV is high and do not take precautions,” said Peter A. Andersen, a professor of health communications at San Diego State University. “People took precautions not only when it was sunny but when it was warmer, and that’s an erroneous calculation in people’s minds. There is absolutely no correlation between temperature and UV radiation.”

There can also be a lot of exposure to UV radiation on cloudy days, he said.

Skiers in the Northern Hemisphere get the highest exposure at midday, and during the late winter and early spring, as they get closer to the summer solstice, Dr. Andersen said. Exposure also increases with elevation.

Readings were generally highest in high-altitude resorts in Arizona and New Mexico, but the highest UV rating — 10 UV index units — was taken at Mammoth Mountain in California. That rating is “just as intense as being smack-dab in the middle of the sun at Jones Beach in June,” Dr. Andersen said.