Final answer:
Chemotherapy is the concept that theorizes the use of chemicals to selectively target microbes without affecting human cells.
Step-by-step explanation:
The concept that theorizes the use of chemicals to selectively target microbes without affecting human cells is called chemotherapy. Chemotherapy is the strategic use of drugs to destroy infectious microorganisms or cancer cells without causing excessive damage to the healthy cells of the host. This concept was first introduced by Paul Ehrlich in the early 20th century, and since then, significant efforts have been made to discover and develop safe and effective chemotherapeutic agents. These agents function by inhibiting critical enzymes in the cells of the targeted microorganisms.