If you live in an older house that had a lot of different residents move in and out over the years, there’s no doubt that the place has a lot of “character”, but one mystery that has been stumping me for some time now are these gross brown spots and streaks on my bathroom walls.

And no, I’m not talking about fecal matter, although this room of the house would be the proper place for it. I’m referring to spots and streaks on the wall that almost look like excessive moisture buildup, and kind of look like dried-up maple syrup with its brownish tint. Sometimes it can get so bad that it looks like someone opened up a can of Coke and sprayed it all over the bathroom walls.

If you have this in your bathroom, then it’s likely one of two things: Smoke buildup from cigarettes, or something called surfactant leaching.

Possibility One: Cigarette Smoke

Of those two potential cases, cigarette smoke is usually the most common culprit. Those spots and streaks are the tar buildup from cigarette smoke, and it gets so thick that it starts streaking down the walls. Pretty gross, right?

What’s even more disturbing is that painting over it won’t do a dang thing, as the tar will still seep through the new coat of paint and give you the same problem. You might have even tried to clean off the tar buildup with conventional house cleaners to no avail, which is perhaps the most frustrating part.

However, I recently discovered that a Magic Eraser does the trick, and it takes the spots right off with a little bit of scrubbing. It makes it even easier if you turn your shower on, close the door, and let the steam from the hot water build up the humidity in the bathroom with the fan off. This will bring out the spots and streaks even more, as well as soften it all up for easier removal.

Note that the Magic Eraser is an abrasive, so you’re basically rubbing a layer off your wall when you do this, and the Magic Eraser may leave a little residue behind. As a result, you may want to clean the wall with a normal cleaner afterward, and then repaint to get things looking clean and even again. It’s a hassle, but at least the tar won’t seep through.

Possibility Two: Surfactant Leaching

If you haven’t noticed brown spots or streaks on your bathroom walls in the past (or anywhere else in your house), but start to see them after recently painting, the problem could be something called surfactant leaching.

Surfactant is an ingredient in latex paint that reduces the paint’s surface tension, giving it more stability and allowing it to last longer. However, the moisture in your bathroom during a hot shower can make the surfactant separate from the paint and seep through, showing up on the surface of the paint as darker spots or streaks.

Luckily, it’s a lot easier to remove than tar from cigarette smoke, as basic soap and water should do the trick to clean up surfactant leaching. It’s also a good idea to make sure you have proper ventilation in your bathroom so that moisture doesn’t build up excessively and causes the leaching.

If you plan on repainting your bathroom at some point in the future, make sure that you give the paint a couple of days to fully dry before introducing any high moisture. Not doing so will allow the surfactant to more easily seep through. From there, keep an eye on the paint for a couple of weeks and if any surfactant leaching occurs, clean it up right away before it fully dries.