The primary cause of winter depression is believed to be reduced exposure to sunlight, which can disrupt the body's internal clock and affect serotonin levels. In India, while winters are not as harsh as in colder countries, the shorter daylight hours during October to December can still contribute to mood changes. Other factors, such as social isolation or the end-of-year stress, may also play a role in exacerbating feelings of loneliness and sadness.