Check the bathroom in this order
Smell the shower pan and drain
Pour a small amount of water into the drain and smell the air that rises. A sour smell points toward the drain or trap, not the walls.
Press along the shower walls
Gently press the surround near the corners. A soft or spongy feel suggests water behind it.
Inspect the caulk lines
Look for dark spotting, gaps or lifted caulk where the surround meets the floor and the walls.
Check the floor around the toilet
Look for discoloration or softness near the flange and where the floor meets the wall.
Test the vent fan
Run the fan and hold a tissue near it to confirm airflow.
Look above the ceiling vent
A brown stain around the roof vent is a sign of leaks from outside, not shower steam.
Common sources of bathroom smell
| Source | What it smells like | What to check |
|---|---|---|
| Dry trap | Sewer or rotten egg | Run water, look for a working trap or a slow drain |
| Hidden mildew behind surround | Musty, earthy | Feel for soft walls and look for caulk failure |
| Toilet seal | Sour, intermittent | Check the water seal and the floor beneath |
| Damp towels and mats | Sour laundry smell | Remove and dry them before storage |
| Roof vent leak | Musty with ceiling stain | Inspect sealant around the vent |
Plumbing smells and mildew smells are often confused. A sewer smell is sharp and sulfurous and tends to come and go with use. A mildew smell is flat and earthy and hangs around even when nobody has used the bathroom. If the smell is stronger after a hot shower, humidity is probably involved. If it is strongest near the drain, look to the trap and the gray tank.
When the floor or walls feel soft, the smell is only part of the story. Wood that has absorbed water may need repair, and cleaning the surface will not change what is behind it. This is the point to find a repair-minded technician, or to bring the problem to someone who deals with RV bodies and roof seals, before deodorizing.
Common questions
Can I just use bleach on mildew?
Bleach on surface mold may lighten it, but it does not dry out what is behind the wall, and it should never be mixed with other cleaners. Fix the moisture source first.
Why does the smell return after cleaning?
If water keeps reaching the area from a leak or from steam, the damp material feeds new growth.
General information for the Denver area, not a quote or professional advice. In an emergency, call 911.