human eye. It may be found behind wallpaper or paneling, on the inside of dropped ceilings, the back of drywall, or the underside of carpets or carpet padding. Piping in walls may also be a source of mold, since they may leak (causing moisture and condensation). Spores need three things to grow into mold: nutrients – cellulose (the cell wall of green plants) is a common food for indoor spores; moisture – to begin the decaying process caused by mold; and time – mold growth begins from 24 hours to 10 days after the provision of growing conditions. Mold colonies can grow inside buildings, and the chief hazard is the inhalation of mycotoxins. After a flood or major leak, mycotoxin levels are higher – even after a building has dried out. Food sources for mold in buildings include cellulose-based materials such as wood, cardboard and the paper facing on drywall and organic matter such as soap, textiles, and dust containing skin cells. If a house has mold, the moisture may originate in the basement or crawl space, a leaking roof or a leak in plumbing pipes. Insufficient ventilation may accelerate moisture buildup. Visible mold colonies may form where ventilation is poorest and on perimeter walls (because they are nearest the dew point). If there are mold problems in a house only during certain times of the year, the house is probably too airtight or too drafty. Mold problems occur in airtight homes more frequently in the warmer months (when humidity is high inside the house, and moisture is trapped), and occur in drafty homes more frequently in the colder months (when warm air escapes from the living area and condenses). If a house is artificially humidified, by the use of a humidifier, during the winter, this can create conditions favorable to mold. Moving air may prevent mold from growing, since it has the same desiccating effect as low humidity. Mold grows best in warm temperatures, , although growth may occur between . Removing one of the three requirements for mold reduces (or eliminates) new mold growth: moisture; food for the mold spores (for example, dust or dander); and warmth since mold generally does not grow in cold environments. Heating, ventilation, and air conditioning (HVAC) systems can produce all three requirements for mold growth. The air conditioning system creates a difference in temperature, encouraging condensation. The high rate of dusty air