What is the origin of the idiom "green around the gills" and when to use it?

The phrase "green around the gills" is an idiomatic expression that originated from sailors who would often get seasick during rough sea journeys. It dates back to the early 19th century, around the early 1800s, and describes the pale, greenish complexion that people can have when they feel nauseous or unwell. It is often used to describe someone who looks pale or sickly, particularly when they are experiencing nausea or feeling unwell. It implies a physical condition where someone appears visibly unwell or experiencing discomfort.