Blue Monday is a myth but winter blues are real—how to cope in the cold months

In 2005, psychologist Cliff Arnall coined the term "Blue Monday" as part of a marketing campaign for a British travel agency to encourage people to book a holiday during the winter. Using a pseudo-scientific formula, the third Monday in January was determined to be the "bluest" day of the year, marked by sadness, low energy and withdrawal from social interaction.

source https://medicalxpress.com/news/2026-01-blue-monday-myth-winter-blues.html