Mold vs. Soot Stains: How to Tell the Difference

Our Answer

What you describe is most likely soot, which deposits on the walls in stripes where framing studs are located, in a flame-like pattern above baseboard convectors, in dots where nails are located, or as circular stains on ceilings above light fixtures. Soot stains on interior walls can be mistaken for mold.
You can test the stain by rubbing it with a little bleach on a paper towel; if the black color remains, it’s soot, and if the color goes away, it’s mold. Repaint soot-stained walls and avoid burning jar candles, which can emit a lot of soot, particularly after the candle has burned down about halfway.