Every homeowner knows the unpleasant experience of discovering something amiss. Perhaps a water stain has formed on the ceiling, or an appliance has suddenly stopped working.

If you notice dark stains on the ceiling or walls of a room, you might fear that it is black mold. However, this might simply be due to a phenomenon known as thermal bridging, or ghosting. While the issue presents more of a nuisance than a serious hazard, it can still help you identify where warm air is leaking out of your home.

The pattern of the staining often seems to follow the framing of the home. Glenda Taylor, writing for SFGate, says you may also be able to discern dark dots pinpointing the location of the nails or screws in the studs.

Ghosting occurs as a result of temperature differentials during colder weather. Ryan Smith, writing for the real estate site Redfin, says you'll create more humid conditions inside the home by showering, cooking, or simply breathing. The home's framing is usually not insulated, so it will be cooler than insulated sections of a ceiling or wall. As a result, the humid air will condense on these areas.

The shadowy stains may be more prominent in certain areas of the home. Taylor says heated elements such as lights will cause dust particles to rise before settling on the cooler wall, creating dark patterns above sconce or other wall-mounted lamps.

It may take some time to notice the staining, but it can become apparent more quickly if there are more contaminants in the home's air. Candles, fireplaces, and incense will all put more soot into the atmosphere, resulting in darker stains. Charles Buell, a Seattle home inspector, says dust particles in the air will also gradually accumulate on the surface.

Ghosting will be more noticeable if the home is poorly insulated, since the stains will form on a larger area. The phenomenon will also be more apparent in areas with greater air movement. Staining can show up around poorly weather-stripped doors, access hatches for attics or crawlspaces, or in areas where insulation is missing.

This issue is a good visual indicator of areas that need some attention to prevent heat loss. Taylor says you'll want to replace insulation or weather-stripping to minimize the temperature variations in your home.

You'll also want to take steps to reduce airborne particulates in the home. These may include replacing a furnace filter, avoiding indoor smoking, or cleaning the rooms more frequently to cut down on dust. Smith says you should also avoid burning candles, firewood, or incense.

A humidity meter will let you know what the humidity levels inside your home are. You should aim to keep relative humidity below 55 percent, using bathroom and kitchen fans to accomplish this effect.

The stains can simply be repainted using a paint designed to mask stains. Taylor says you might opt for a darker color, since staining will be less apparent against this hue.

If the problem is occurring in a bathroom or other area with higher humidity, it might actually be black mold. If you suspect this is the case, have the stains tested by a professional. Smith says you might be able to address the problem by scrubbing it away with a bleach solution. You should also make sure your bathroom ventilation is adequate and that you use mold-resistant paint in this room.