If you don't keep your drains clean, several problems can occur:

1. Clogs: When hair, grease, soap scum, and other debris build up in your drains, it can cause clogs that block the flow of water. These clogs can be difficult to remove and may require the drain cleaning services of a plumber.

2. Bad odors: As debris accumulates in your drains, it can produce a foul smell. This can be unpleasant and may indicate a serious problem, such as a blocked drain or a broken sewer line.

3. Water damage: If your drains are clogged, water may back up and overflow, potentially causing water damage to your home. This can be costly to repair and can lead to the growth of mold and other harmful bacteria.

4. Health hazards: If your drains are not clean, bacteria and other harmful microorganisms can grow and potentially cause illness. This is particularly true in areas where food is prepared, such as the kitchen sink.

To keep your drains clean, you should regularly clean them using a mixture of hot water and vinegar, or a commercial drain cleaner. You can also use a plunger or a drain snake to remove any clogs that may have formed.