A bad smell coming from food is a warning that something is wrong with it and you shouldn't eat it. A musty smell coming from your bathroom is also a warning. It's a signal that you need to make some changes to the room and to your showering routine.
The musty smell in your bathroom is caused by mould or mildew. These fungal growths cause the same musty odour in damp basements. They thrive in moist, poorly-ventilated areas, especially in bathrooms. Follow your nose to find the mould. Common locations for growth include inside the shower, on walls behind towels or picture frames or on the ceiling. Mold and mildew are typically dark coloured and grow in feathery-looking patches.
You can't ignore mould and mildew in your bathroom. Not only is the musty smell unpleasant, but it can be hazardous to your health. People who are sensitive to mould experience headaches, nosebleeds, respiratory problems and nausea when exposed to mould spores. Mildew can stain grout between tiles and damage paint. Over time, it can eat into drywall and spread throughout your home, which can lead to serious damage and health problems over time, requiring intensive work to remove.
Getting rid of the fungus in your bathroom will take care of the musty smell. If mould is growing on tile or fibreglass, use a solution of 1 cup of bleach in 1 gallon water. Soak a sponge in the mixture, and wash away the mould. For mould growing on paint or wood, dilute the solution to 1/4 cup bleach in 1 gallon of water. Once the mould is washed away, dry the area as quickly as possible. If you have mould growing in a patch larger than one square foot, contact professionals to remove it and evaluate the damage left behind.
If you don't make any changes to your bathroom, mould and its musty smell will return. Install an exhaust fan and run it while showering to pull excess moisture from the air and make the room less hospitable to mildew. Keep a squeegee in the shower, and use it to wipe down the walls and shower curtain after each use to prevent mould growth in the shower. Always hang wet towels so they dry more quickly; leaving them crumbled on the floor can lead to mould growth on the fabric.