A chemical is considered toxic when that chemical may be harmful to the environment around it and to the human health if it is inhaled, swallowed, or if it is absorbed through the skin. Some warning symptoms with being around toxic chemicals are headaches, dizziness/lightheaded, problems with attention span, impaired balance, "pins and needles" feeling or numbness.

Resources: "What Is a Toxic Substance?." Web. 15 Feb. 2010. <>. (image and information)