Dark spots in a shower are usually surface growth on caulk, grout or a curtain, and cleaning is often enough. The exception is when the spots keep coming back, when tile is loose or the wall feels soft, which points to a leak behind the wall. This guide helps you tell the two apart and decide what to do.
Why showers grow it
A shower stays wet, warm and covered in soap film, which gives growth moisture and food. Caulk lines, grout and the bottom of the curtain stay damp longest, so growth shows there first.
That is normal and often manageable. Weekly cleaning, a squeegee and a working exhaust fan prevent most of it. Growth that appears inside the caulk itself is a sign the caulk is past its life.
A quick checklist: surface or hidden
Check these points before you decide.
- Does cleaning remove the spots and keep them gone for weeks? That suggests a surface issue.
- Does the caulk look dark all the way through? Replace it.
- Are any tiles loose, hollow-sounding or cracked? Water may be getting behind them.
- Does the wall near the shower feel soft, bubbled or stained on the other side?
- Is there a musty smell in an adjoining closet or room?
Two or more yes answers in the last three points are a reason to get a moisture reading.
What each sign usually means
These are common patterns, not diagnoses.
| Sign | Likely meaning | What to do |
|---|---|---|
| Dark spots on grout, clean off | Surface growth | Clean, dry, improve ventilation |
| Dark caulk that does not come clean | Caulk has failed | Remove and recaulk |
| Loose or hollow tile | Water behind the tile | Open and inspect |
| Soft drywall outside the shower | Hidden leak | Meter reading and likely repair |
| Stain on the ceiling below | Leak between floors | Call and tell the building manager |
Cleaning the right way
Wear gloves, ventilate and scrub with detergent and water. Rinse and dry the surface. Replace caulk that is darkened throughout, using a mildew-resistant product after the joint is fully dry.
Keep the fan running for a while after showers and wipe the walls. If the fan is weak or noisy, replace it. Fixing the humidity solves more cases than any cleaner.
Showers in Tarzana's condos and apartments
Warner Center and Ventura Boulevard are lined with multi-unit buildings, and Reseda alone has more than 24,000 households in ZIP 91335. A shower leak in a stacked building can stain a ceiling below, so tell your manager before you repair anything.
If you plan to replace the tub surround or tile, ask the Los Angeles Department of Building and Safety whether your scope needs a permit, and check the contractor's license with the Contractors State License Board. California requires a license for jobs of $1,000 or more in labor and materials, and a bathroom rebuild passes that quickly.
Grout, caulk and curtains behave differently
Grout is porous, so it holds soap and water in its surface and darkens first. Caulk is flexible and sits at the joints where water pools, which makes it the first thing to fail. A plastic curtain collects residue along its hem and holds moisture against the tub edge.
Because the materials differ, the fixes differ. Grout can often be scrubbed and resealed, caulk should be replaced rather than cleaned over and a curtain liner is cheaper to swap than to fight.
Ventilation is the quiet cause
Many bathrooms in older Tarzana homes have a small fan or none at all. A fan that moves little air leaves steam on the walls, and the room stays humid long after the shower ends.
A simple test is to hold a square of toilet paper against the fan grille. If it does not cling, the fan is weak or blocked. Cleaning the grille or replacing the fan costs far less than repeated scrubbing and prevents the cycle from starting again.
A simple weekly routine that works
Small habits keep growth from taking hold, and they cost almost nothing. Try this routine for a month and see whether the spots return.
- Run the fan during the shower and for at least twenty minutes afterward.
- Squeegee the walls and glass, then wipe the tub edge.
- Hang the towel and curtain so they dry fully.
- Scrub caulk lines with detergent and a soft brush once a week.
- Check for loose tile or a spongy wall every few months.
What to tell a crew when you call
Describe where the spots are, how long they have been there and whether anything feels soft or smells musty. Mention whether the shower shares a wall with a bedroom, closet or neighbor. If a stain has appeared elsewhere, say so, because that points toward a hidden leak and mold remediation after the cause is fixed.
When a crew should look
Call if the wall near the shower is soft, if growth keeps returning after cleaning or if a stain appears on a ceiling below. A crew reads moisture, opens the wall if needed and removes affected material following ANSI/IICRC S520. See mold remediation for how that works.
A wet wall cavity first needs water damage repair after drying, and neighbors in Woodland Hills and Sherman Oaks can call the same line.
Frequently asked questions
Symptoms are a question for your physician, not this site. For the home, dark caulk is a sign the joint is past its life, and replacing it is usually the fix.
If the growth wipes off and the caulk is intact, cleaning can work. If the caulk is darkened through or peeling, replace it.
Report both to your manager in writing. A stain below suggests a leak that the building must fix, and you should document it.
Yes. Moisture can travel into adjoining walls and ceilings, so a smell in another room is a clue worth following.
There is no fixed schedule. Replace it when it cracks, peels or stays dark after scrubbing, which is commonly every few years depending on use.