红发是指多种色调不一的发色，包括较深的橘红色、橘色，以及铜色。

在人类族群中，大约有1%到2%的人口拥有红发。较常出现在北欧与西欧，在这些地区占约2%到6%；欧洲其他地区，以及亚洲和非洲则相对少见。汉族群中，红发虽然很少，可是还是会发生。

Red hair occurs naturally in 1–2% of the human population. It occurs more frequently (2–6%) in people of northern or western European ancestry, and less frequently in other populations. Red hair appears most commonly in people with two copies of a recessive allele on chromosome 16 which produces an altered version of the MC1R protein.