Cotton curtains should generally be washed every 3 to 6 months to keep them clean and fresh. However, the washing frequency can depend on where the cotton curtains are used. For example, if they are in the kitchen or a room with a lot of dust, you might need to clean them more often. If someone in your home has allergies, washing cotton curtains more regularly—maybe every 2 to 3 months—can help remove dust and allergens. If the cotton curtains are purely decorative and not touched or moved much, you can wash them less often, like twice a year. Before washing, always check the label on your cotton curtains. Some might need hand washing or a gentle cycle in the washing machine. It's also a good idea to shake them out every few weeks to remove surface dust, which helps you wait longer between full washes.