Everybody loves a good hot tub. Skiers in particular love a good hot tub. But beneath all that steamy goodness lurks real danger. A new study, published in the American Journal of Preventive Medicine, found that emergency room visits sustained in hot tubs whirlpools or spas more than doubled from 1990 to 2007. Most of the injuries were slips and falls; overexposure to heat was another big culprit. Scary stuff.