What are the main causes of a thick, greasy, yellow tongue coating?

A thick, yellow, and greasy tongue coating may result from improper diet, such as frequently consuming large amounts of raw, cold, or irritating foods, leading to spleen deficiency and impaired spleen function in transporting dampness. It could also be caused by prolonged exposure to a humid climate or chronic emotional stress, low mood, or depression, resulting in internal accumulation of damp-heat. If accompanied by symptoms like indigestion or intestinal dysfunction, these factors may contribute to the condition. Timely differential diagnosis is recommended.