If you have ever removed wallpaper, you know what they are talking about. We install wallpaper with wallpaper paste (yes Mr. Obvious) Wallpaper paste is WHEAT paste. Just imagine that you leave a piece of bread sit out......That mold will find the wallpaper paste to be a yummy environment.
For More Information
http://www.wtae.com/article/is-wallpaper-in-your-home-making-you-sick/10217478
Toxins from fungus growing on wallpaper can easily become airborne and pose an indoor health risk, researchers say.
"We demonstrated that mycotoxins could be transferred from a moldy material to air, under conditions that may be encountered in buildings," said study corresponding author Dr. Jean-Denis Bailly. "Thus, mycotoxins can be inhaled and should be investigated as parameters of indoor air quality."