A common source of smells is the organisms that usually reside in the sewer of your bathroom. These organisms make a home in your bathroom and generate sewer gas inside the fixtures, which form moulds in your bathroom. Here are some ways to ways to prevent bad odour from the bathroom 1. Ventilate The Space, 2. Clean Regularly, 3. Fragrance Lamp or Scent Diffuser, 4. Prevent it from Moulds, and 5. Keep Towels Clean and Dry.