If you find mold on a surface, you can usually prepare a mixture of bleach and water, wipe up the mold, and be done with it. But sometimes, the mold will come back! You could certainly bleach the area again, but this may just be a temporary fix if there is a larger problem at-fault for the mold growth. Here are three possible reasons why the mold keeps coming back.
There's mold beneath the surface, too.
You may only be cleaning mold off the very surface of the item when really there is a larger mold colony beneath the surface. The colony keeps growing, so you removing part of it with bleach does little good. This can be the case with walls. Removing mold from the surface of the wall only works temporarily if there is also mold behind the wall! In the long term, you may have to remove the drywall, clean out the mold behind the wall, and build a new wall.
It's too humid.
If the area is really humid, mold growth becomes so much more likely. Some mold spores may remain in the air even after you clean up the mold with bleach. If they settle on the surface, they can get all the moisture they need from the air to blossom into full-grown adult mold. Installing a dehumidifier can work wonders in situations like this. Also make sure that if you have exhaust fans, you are using them. If your old exhaust fan is not removing moisture fast enough, have it replaced.
The area does not dry fast enough after becoming wet.
If the mold is appearing in a shower, sink, or other areas that become wet on a regular basis, then the problem might be that the area is staying wet for too long after you use it. (This is closely tied to the space being too humid. If the air is too humid, moisture won't evaporate from the surface fast enough.) You can alleviate this problem by drying out your tub or sink after you use it. You may also wish to have the slope of your shower or sink altered so that water does not pool in the bottom of it.
If mold does not go away easily, try to reduce your humidity, address lingering moisture, and check behind the surface. Contact a mold removal company like Servpro Of Washington County for assistance if you still can't permanently get rid of the mold yourself.