What are the ways in which harmful substances from the surrounding world enter the human body?

In the human body, harmful substances, first of all, can get along with food, eating something where harmful substances are present, a person will receive a portion of something bad for the body. Also, harmful substances enter the body through the respiratory tract, for example, inhaling combustion products, gasoline vapors or emissions of harmful industries is very dangerous – you can get poisoned or even die, this route is considered the most dangerous. More harmful substances can get absorbed through the skin.