热病，是因高温而造成的疾病。

通常引致热病的情况很多，可能是环境温度高而导致热病，亦可能是病患自身体温过高，或是长期暴晒的情况。热病也有可能因天气热而致流汗多，并出现脱水而令身体无法反应所致。热病通常都会发生于夏天。

Heat illness or heat-related illness is a spectrum of disorders due to environmental exposure to heat. It includes minor conditions such as heat cramps, heat syncope, and heat exhaustion as well as the more severe condition known as heat stroke.