For most people, black spots in the shower caulk are an eyesore. For some households, they're more than that. If someone in your home has asthma, a mold allergy, chronic lung disease, or a weakened immune system, the CDC says mold can hit them harder. People with asthma or mold allergies may have severe reactions, and people who are immune-compromised or have chronic lung disease may get lung infections from mold.
That changes how I think about a moldy caulk line. It's not just about looks anymore.
Why the black keeps coming back
This is the question I hear the most. Typically, scrubbing isn't going to remove it. Even if it looks like it did, the mold is still embedded in small little pores in the caulk. It will keep regrowing until the caulk is completely removed and reapplied.
The EPA says something similar about porous materials in general. Mold can grow in the empty spaces and crevices of porous materials, so it can be difficult or impossible to remove completely.
Why a fresh bead over the top doesn't help
The most common mistake I see, from DIY jobs and cheap jobs alike, is new caulk applied over caulk that was already poorly applied or deteriorated, thinking it's going to make it better.
In a sensitive household, that's the worst of both worlds. The shower looks clean, but the mold is still there underneath the new bead (the line of caulk). The EPA's mold cleanup guide is direct about it: don't paint or caulk moldy surfaces. Clean up the mold and dry the surface first.
So the order matters. The old caulk comes all the way out. The joint gets cleaned and dried. Then the new sealant goes on. I walk through that whole process, with a North Park job as the example, in Why Does My Shower Caulk Keep Cracking or Turning Black?
Who should do the cleanup
If you're the one with asthma, allergies, or a weakened immune system, the CDC's advice is not to take part in mold cleanup yourself. Have someone who isn't at risk handle it. The CDC also says people who are immune-compromised or have asthma or COPD shouldn't be in the home while mold is being cleaned, so plan to be out during the work when that's possible. If you have health questions about mold, your doctor is the right person to ask.
If that sounds like your household, a parent, a spouse or a kid with one of those conditions shouldn't be the one scraping out a moldy shower.
Check what's behind it before anyone scrapes
Press on the wall or floor right next to the failing caulk. Does it feel soft or crumbly? Does a stain get wet or grow after showers?
If the area around the failing caulk is soft or wet, it can sometimes be remedied by a handyman if it's a small area. If it has led to extensive mold growth, or more damage you can see without opening up the floor or wall, it may be better suited for a restoration company (a specialist in water and mold damage). The EPA notes that mold areas larger than about 10 square feet may call for professional help.
Keep it from coming back
In a well-ventilated bathroom that's used and kept up consistently, caulk lasts a lot longer. Poor ventilation is where it fails fastest. The EPA's advice is to run the fan or open a window when you shower, and to keep indoor humidity below 60 percent, ideally between 30 and 50.
If your fan isn't clearing the steam, that's worth a look. Here's when a bathroom fan just needs a little care.
What it costs
Recaulking a tub or shower area is $180, or +$90 as an add-on to another job on the same visit. That's old caulk out, cleaned, and fresh 100% silicone. Prices shown are labor only. Caulking typically has a materials cost of about $15 per visit, depending on the product used, which is added to your final quote. More on the shower recaulking page and my pricing page.
Send me a few photos
If the black keeps coming back, text a wide photo of the shower, a close-up of each caulk line and your ZIP code. Let me know if someone at home is sensitive to mold, and I'll tell you what I see and what the next step looks like.
Call or text (619) 815-7588.