As we anticipate a break from the latest heat wave, consider this: it could be the hotter nights are more dangerous than the hotter days. Climate and health experts warn that nighttime temperatures no longer provide the solace they did a century ago and are exacerbating the risks of sickness. Nighttime should offer a natural relief for those without artificial cooling, when the sun disappears and temperatures drop. But that doesn’t work if even the low temperatures stay high. “When it’s hot out, your body has to work pretty hard to keep itself cool,” says Brooke Anderson, an epidemiologist at Colorado State University. “If it gets very hot at night and you continue to be exposed to it, your body does not get a chance to rest.” Nightime temperatures, in recent years, have increased at a faster rate that daytime highs.