Mold cleanup can be painstaking. The sources of the mold have to be located, the areas have to be contained, material removed under controlled circumstances, then vacuumed, washed and vacuumed again. Drywall is porous, and if there's mold, it is all over the place. Hard furniture such as tables can be cleaned, but soft furniture such as couches have to be gotten rid of. Air tests are taken before the job begins and after it has been completed to determine the level of mold spores. Mold thrives most often in moist conditions. Moisture combined with a nutrient source such as soil, dust and products containing cellulose or other dead organic matter provides the ideal environment for colonization. Though indoor mold always has been a problem, it has been aggravated by changes in construction techniques brought on by the energy crisis of the 1970s. Efforts to create energy-efficient houses without accompanying efforts to regularly exchange the air inside have been linked to a dramatic increase in cases of asthma in the last three decades.