Suddenly the walls in my dressing room have black mold over all wit

Does it share a wall with a bathroom? Roof directly overhead? Check both for leaks.

Didn't quite get your whole thought there. This is the time of year when it will happen because there is a lot of humidity in the air.

You can use a product like Clorox Cleanup to remove the mold from surfaces but you have to, as Robyn said, find the cause of the excess humidity or the problem will continue.

Yep Mold is a major health risk. Please contact a professional to deal with the mold before doing anything.

Oh dear, mold can make you very sick. I would call a professional if its mold and not mildew. Heres a video on how to tell the difference.... https://www.youtube.com/watch?v=1rGiSspDkxM

https://www.youtube.com/watch?v=69axemMuM3g

Mold is dangerous. Black mold is especially dangerous. If it is black mold and not mildew (see above video) don't mess with it. Don't try to clean it yourself. Call a pro. At least in New York, mold abatement is now treated very much like asbestos abatement because they can cause similar health problems. And make sure to find and fix whatever leak is allowing moisture to collect on (or behind) those walls.

Bleach and then find your leak

All mold is toxic when enclosed. To be safe, remove the drywall completely and replace. First find out why it's growing. You probably need to ventilate the room or get a dehumidifier. Mold inside a home is toxic!

I lived 14 months in a home where mold grew under the vinyl flooring caused from a bathroom flood. I became so ill, I thought I was dying and never was sick a day before moving in the new apartment. After 14 months I call a certified air quality contractor who tested the indoor air and outdoor air for mold spore count. The test results came back with very high levels of a mycotoxin mold called penicillium aspergilious. In order to save my life, I had to walk away from everything, family pictures, antiques, clothing, everything. I had to put my little Bella down. With no help or family, at 64 I found myself living in my car for two years. I have shelter at the moment but don't know for how long. Trust me when I say to remove the infested area. Mold is a living microorganisms. It is so small it can go through concrete. Clorax will not get rid of it. Once disturbed, it will attack the body through the skin and then your central nervous system. My life will never be the same!