Dangerous exposure to a chemical can occur in a variety of ways. They can be inhaled through the nose or mouth, absorbed through the skin or eyes, ingested through eating if hands have not be washed, or absorbed into the body through cuts or punctures. How the chemical enters the body can sometimes affect the speed and severity of the response that occurs. 

For example, asbestos is only harmful when it is inhaled or ingested. On the other hand, some chemicals can be toxic no matter how they are encountered. You should always take precautions when working with toxic chemicals.