Drains can become clogged due to the buildup of various materials over time. Common culprits include hair, soap scum, grease, food particles, and foreign objects like cotton swabs or small toys. In kitchens, fats and oils can solidify and create blockages. In bathrooms, hair and soap residue are frequent causes. Additionally, tree roots can infiltrate outdoor sewer lines, leading to severe clogs. Regular maintenance and mindful disposal of waste can help prevent these common causes of drain clogs.