How do you get rid of mold under the bathroom sink in a vanity?

clean the area well with hot detergent/water and put a fan in the cupboard to dry it -- and find out where you have the leak! and don't use 'bleach' --- 1. it only removes the COLOR of the mold spores and those that have grown into the paint or the wood are still there --- Concrobium is the product to use -- any hardware store will have it -- but find / fix the leak first http://www.concrobium.com/how-to-fight-mold/where-is-your-mold/bathroom/?gclid=CjwKCAiA8vPUBRAyEiwA8F1oDNtMgYjsHyFSLtZVuAQYP-AxSSimiCQEtvLfegGzir9R1dlFRDm0WxoCMzkQAvD_BwE

it's expensive, but it works!

You have a leak somewhere - the walls are wet and that is why you have mold. Unless you address the leak first, no matter how many times you "clean" the mold off and treat the wall areas where it grows, it will come back.

Thank you so much!

I would use 10% bleach and water solution to clean it up, and an old rag/sponge. Then use vinegar to prevent it from coming back.

You had better find the leak to prevent it from coming back and ruining the whole vanity. I would start by looking at the pipes, and then the caulk along the top edge of the countertop. You could wrap the pipes in paper towel, leave for a day or two and then take it off noting if any water has penetrated the towel. Is the sink draining properly, if not clean out the p-trap, the sink plunger under the sink, and where the P-trap goes into the wall with one of those hair removing plastic snakes. Then use fresh teflon tape on the pipe ends to ensure a good seal.

I think the more pressing issue is to find out why it’s happening. Is there water dripping somewhere along the back?