Can you see evidence of water damage? If there’s nothing visibly apparent in adjoining walls/floors/ceilings you’re probably ok. I’m not sure how long mold resistant caulking has been around but even if it was done correctly and they used the appropriate kind it loses it’s resistance over time, I think most of the silicone anti-mold caulks typically site like 7-10 years. I would cut/scrape the existing caulking away with a utility and putty knife and scrub everything down with a bleach solution and then reapply caulking that’s specifically for bathroom use once everything is cleaned and dried. How is the ventilation in the bathroom? Do you have a ceiling fan in the bathroom or is there good ventilation? Usually want to leave a fan on for 10-15 minutes after use so that it clears most of the moisture out of the air.

Ideally, remove all the caulking. All of it. Clean w 50/50 bleach/water. And do it over. And be thorough . Sashco Lexel White adhesive caulk. mold resistant, sticks around a long time, works on wet surfaces. It isn’t cheap tho. 20-25 bucks for a 10oz tube. If that’s too costly, GE Supreme Silicone is a good product but you absolutely have to get the old caulking out first. That’s about ten buck USD a tube.

If you can’t remove it all…. Remove all old loose caulking. Clean up caulking with a 50/50 bleach/water mixture. Let dry well.Then go back with what was there - silicone or adhesive caulk, etc. Large gaps need something like backer rod to fill the majority of the void. Is it a tiled shower stall or is it paneled? Is the gap at the tub/panel joint? Where is the gap worst at? Fill the tub w water halfway, then do the work. Preloading the tub with some weight helps a bit with the tub/panel joint cracking.

Fixing mold can potentially be stupid expensive, but my experience is in commercial settings, not residential. Leaking around the tub can mean up to and including ripping out tub, greenboard, and exposing the studs to either replace or treat them. It likely won’t need to go that far.

Leave door open when not in restroom. Install a fart fan.

so, i was imagining doing it myself because i have in this situation. others have good advice in here, so rather than being prescriptive, i’ll just say what i did and with what. i probably started by watching a youtube video. if there’s a this old house / bob vila one, those are fast and with just the right amount of detail for me.

getting rid of old crap, the most critical part:

• cut away old
• scrub surface with soap and water
• sanitize with bleach solution

i took a utility knife and ran it down the horizontal and vertical planes of the joint to cut out all the old crap. pulled it away and tried to get as much of it removed/thrown away. then i came in with some kind of detergent / soap and scrubby pad, like brillo. something tough, but you don’t want to scratch the tub and tile surface so don’t use like metal. pumice stone is crazy effective on porcelain. scrubbed away as much detritus and mold as i could. i always use a solution of 15% bleach in water, as this is a recommendation for sanitizing food prep surfaces (total overkill in this situation). most household products with bleach are 5-9%. bleach works best to kill when it has a longer “contact time” and isn’t getting chemically bound onto some larger chunk of organic material that should have been wiped away. so when i’m sanitizing an already scrubbed surface, i mist it with my 15% and let it evaporate (open doors/windows) for maybe 15+ minutes. then i come back and depending on how it looks, i give it another soap+water scrub+bleach mist again, or just call it good.

the caulk application thing is fast, but easy to make a mess so i definitely watched a few videos of how people lay beads and what tools they use/prefer, plus their little tricks for slicing open the tip. caulk guns work, though can be fast for first timers. so a practice bead on some cardboard box is a cool move. usually there’s a little plastic corner trowel type of thing sold for $1 next to the caulk supplies to run over the bead and push it into the corner/make it look clean. the product you buy will have the cure times listed for how long to let it sit before you run water over it.

EDIT: as far as DIY projects go, this is pretty cheap (~$20 if you have none of the tools/materials) and most of the time between start to “ready to show” is spent letting things dry/cure, so you can take breaks and watch more DIY videos.

These comrades above me got the right idea. I did this the other day and it’s really not that bad. The hardest part is cleaning up the old shit. It can really be a pain on your wrists if you have sensitive ones like me so be careful to use good technique and take breaks so you don’t strain yourself too bad.

All I gotta say is “Nice caulk!”