It sounds like the exposed MDF edges were not properly sealed, which could indeed lead to moisture absorption and swelling, especially in areas like bathrooms where humidity levels are higher. Ideally, any cut edges of MDF should be sealed with a suitable primer or sealant to protect against moisture penetration.

To address the issue now, you have a couple of options:

1. Re-sealing the edges: You could apply a suitable primer or sealant to the exposed MDF edges to prevent further moisture absorption. This might help mitigate the swelling issue.

2. Caulking: Caulking the baseboards to the floor can help create a barrier against moisture and prevent water from seeping in between the baseboards and the floor. This can be an effective solution, especially if the swelling has already occurred and you want to prevent further damage.

In either case, it’s essential to ensure that the affected areas are thoroughly dry before attempting any repairs or modifications to prevent trapping moisture and exacerbating the issue. If you’re unsure about the best approach or if the damage is extensive, it might be worth consulting with a professional trim installer or contractor for personalized advice and assistance.