Nontoxic is defined as not being harmful at concentrations normally used. However, most people believe that it means a substance is innately harmless — and this just isn’t so. In fact, according to the U.S. Federal Hazardous Substances Act, a substance can legitimately be called “nontoxic” if it does not cause acute (sudden-onset) health effects. By this narrow, legal definition, some products that cause long-term problems such as cancer or birth defects, or are slow-acting or accumulating poisons, can be called “nontoxic.”