The Clue Darkens after exposure to the sun
The Answer TANS
The answer "TANS" fits the clue because it describes what happens to skin when it is exposed to the sun. When you spend time in the sun, your skin darkens or tans as a way to protect itself from UV rays. This process is a natural reaction and is common for many people who enjoy outdoor activities. Therefore, "tans" is the perfect word for this crossword clue.