Have you ever noticed how it can be really hot on the sidewalk, but comfortable and cool under a tree? In a city, where there are lots of buildings and roads, it can get hotter than the countryside. There is a name for this: the urban heat island effect. We wanted to know whether the urban heat island effect affects everyone in cities equally. We looked at data about 175 big cities in the United States. It turns out that people of color have higher exposure to the urban heat island effect than white people in all but six of these cities! Poor people also usually have higher exposure. Climate change is going to make hot days even hotter. We hope that city leaders use our data to help neighborhoods prepare for climate change.