VOCs are Volatile Organic Compounds. VOCs can be released by human or natural source, and can react with the atmosphere to form ground-level ozone, and to a lesser degree, acid rain. Some VOCs, like the fumes from numerous interior products (glues, paints, cabinets, carpets, and pads, furniture, etc.) are toxic, and can cause a range of health problems from occasional headaches to allergic reactions, depending on the concentration and the sensitivity of the individual. "Least toxic" products are those which contain levels of VOCs below what the EPA or other credible sources have determined to be safe levels. In some cases, a "least toxic" product may be preferable to a "non-toxic" product for reasonable performance. For additional assurance, consider mechanical ventilation with an air-to-air heat exchanger that gives fresh air without wasting heat.