A white residential ceiling exhibits distinct dark, parallel stripes, often found along joist lines. This clear visual demonstrates thermal tracking, or 'ghosting,' where soot and dust adhere to colder surfaces, as explained in our article: 'Thermal Tracking ‘Ghosting’: Why Your Walls Have Black Stripes'.

Black Lines on Your Walls and Ceiling? It’s Probably “Thermal Ghosting” — Not Mold

Feb 17, 2026

Perfectly straight black lines running along ceiling joists or wall studs are almost always “thermal tracking” — soot deposited on cold spots in your framing, not mold. Learn what causes it, how to tell the difference, and whether you need a pro.