Types of ultraviolet rays

Ultraviolet rays consist of two types, UV-A and UV-B, which cause different reactions in the skin. Exposure to UV-B rays causes the skin to become red, stinging, and blister-like a few hours later; melanin production begins 2 to 3 days later, once the redness starts to subside. UV-A rays do not cause redness or inflammation like UV-B rays do, and melanin production begins immediately after exposure. They also have the effect of making existing melasma darker.