There it is: the dreaded ceiling stain. What do you do? Call a roofer, a plumber, or a painter? If you call the wrong person first, they may not be able to help you, and you may have wasted time and money. Before you call anyone, do a little research on your own.

Once you understand the cause, you may also find that the solution is something you can handle yourself. If you do need to hire a pro, at least you’ll be reasonably certain of which type of firm to call.

Don’t try to fix the stain or any damaged drywall or plaster until you’re sure you have the moisture problem licked. When you’re sure you’ve solved the problem, repair the walls and ceilings, but make sure you use a stain-killer primer before repainting. Otherwise, you may find the stain bleeds through the new paint.

Here are answers to some of the most common questions about ceiling water stains:

Q I have a stain on my living room ceiling. The ceiling is directly beneath an upstairs shower. I re-caulked the shower, and the problem is still there. Do I need a plumber to replace the pan under the shower?

A Probably not. You were correct to suspect the caulking. It is usually the culprit. However, simply adding another layer of caulk over the old caulk usually does little good. Instead, you must remove the old caulk completely, clean and dry the surfaces and then recaulk.

Q One pipe under my sink is always wet. Water drips from it onto the floor and has left a stain on the ceiling below. Should I call a plumber?

A Check to see if the pipe is wet all over or just below a seam. If it’s wet all over, the problem can be solved by insulating the pipe. This is an easy do-it-yourself project. Your local hardware store or home center can help you identify the   right insulating product to use. If the moisture shows up just below a seam, you probably have a leak and should call a plumber.