It seems to me that the problem is more than a dehumidifier totally remedy.

You should probably contact someone who specializes in mold issues to determine the problem.

I think you've said you live in SoCal. There should be no need for a dehumidifier under normal conditions. The humidity source needs to be found and stopped .

I'm going to take two guesses.

-Is there a bathroom with a shower adjacent to this room? Is the bathroom door kept closed until the humidity from use has cleared either using an exhaust fan or an open window (using either may take as much as 30 minutes).

or,

-Is the outside side of the wall fully exposed to the air? Is the wallboard on the inside soft or spongy at all? I'm going to guess that dampness is coming in, either through the wall or the floor. If through the floor, how's the drainage on the other side of the wall? Is the ground often damp? If through the wall, I'd suspect a leak through the window/flashing or down the wall from higher up.

Call your homeowner's insurance agent, ask how to handle it.

I do live in So. Cal. My neighbors across the way from me have the same issue. Things getting moldy in their closet. They use the container dehumidifiers..that is where I got that idea from.

Yes the outside wall of the back end of my condo which is actually all master bedroom is fully exposed to air. I did feel the wall that the dresser was against but it wasn't like it was moist and mushy or anything.

I've notice I've had the mold shoe issue on both sides of the room...When I first noticed it, I had a wooden box that I kept shoes stored in...of course all the bottom shoes were ones that never got worn, so when I pulled the box out all the shoes were moldy....

There are dressers on the other side of the room I'm going to pull out and see if their backs are moldy too.

ETA: yes there is a bathroom next to the bedroom room, it has a pocket door but it's kept shut 99% of the time. I do open my window often (bedroom window) for fresh air...Bathroom doesn't have a window, just a fan.

If you use the bathroom fan religiously and keep the door closed, then my money bet is that water is coming in from the outside. Maybe through the floor if you're on the ground floor, maybe through the wall.

Either way, it's potentially "water damage" and I'd call your insurance agent for guidance. Maybe it's not covered but it's a start. I'd also check with the HOA, how many others have had the issue, what has been discovered?

Good luck

My basement gets damp in the summer. Running the dehumidifier turns it into a desert, and I am in the humid Northeast.

You need to find the source of the moisture. You are only seeing a small portion of the damage. The inside of the wall behind the dry wall could be growing a lot of mold and black mold could be in the mix. Don't just treat the symptoms fine the cause and cure it. The property could be improperly leveled and directing run off water towards the foundation of the house instead of away. Is there any type of flower beds or plants along that wall? They will hold moisture against the house. We had a similar problem in our old house. It was because of bad leveling and a flower bed that was too close to the foundation. A French drain was needed to correct the problem.

Have you reported this to the board of directors? That's your first step.

Yes it will help. Always good advise to think about excessive humidity and where it is coming from. Most basements in my world need one running summers.

If the exterior wall is brick make sure the landscapers haven't covered up or raised the ground level over the weep holes. The ground should be several inches below the bottom of the weep holes to ensure proper drainage.

Few structures, and especially few residential structures, have been built of brick in California in the last 100 years. When there is brick on an exterior wall, it's a veneer for appearance and not structural.

I do think drainage and dampness incursion from below should be pursued with the association and investigated by a pro, as others have said.

I check the other dressers on the other side of the room..same thing mold growing up the back of them. Sons room doesn't have any thing against the outside wall for me to check...Wondering if I should turn his dresser to see what happens. His dresser has legs and doesn't sit on the floor...not sure if that will make a difference. I wonder if I tape plastic against his wall if moist will build up.

I did check with neighbor and in their closet, not only on the floor but they had stuff up on shelves that got moldy...so he was thinking it was moisture coming "down"...?? who knows, but I am sending pics to property management and then going from there.

My house, which was 1/4 mile from the beach in north San Diego county, had a problem with mildew in one room. There was never any external source of moisture on my property that could be identified -- no leak under the house ever found, or pooling or standing water, although I did water the fruit trees (did not have grass). No sign of a roof leak. I assumed it was just from the frequent fogs, perhaps how the house was situated, and the tree shading that corner of the house. This 1948 house did not have AC and only a small propane heater. I had to make a practice of washing the walls and window frames down at least twice a year with weak bleach water to keep the mildew at bay. Once mildew gets into drywall or plaster, it is very hard to eliminate.

ETA that I have had a leak from around a vent pipe in the roof, where water traveled down the wall and showed up via mildew stains coming through the wallpaper. Sounds like your condo building might have a major problem with water penetration.