The weather is very hot. Can people turn black without the sun?

No, it won't turn black unless it is irradiated by ultraviolet rays in the sun. The reason why the skin turns black is because there is a kind of "melanin protoplasm", also called "pigment mother cell". Melanin is secreted by pigment mother cells. When ultraviolet rays irradiate the skin, the skin will be in a state of "self-protection". Stimulate melanin by ultraviolet rays, activate tyrosinase activity and protect our skin cells. Tyrosinase reacts with tyrosine in the blood to produce a substance called dopa. Dopa is actually the precursor of melanin, which is oxidized by tyrosine and releases melanin. Melanin moves through the metabolic layer of cells, forming freckles, sunburns, dark spots and other shapes on the skin epidermis.