Mold

Mold occurs naturally and can grow almost in any place that is warm and damp. Experts have identified more than 100,000 species of mold; at least 1,000 are common in the United States.

While the most common molds generally aren’t hazardous, some types are blamed for headaches, fatigue and respiratory problems.

In many countries, school districts are finding allergy-inducing mold in walls, on carpets and near ventilation systems.

While one study blames aging buildings and mold-promoting construction techniques, other findings suggest the problem is due to a lack of proper ventilation in newer schools.