Which of the following is NOT considered a type of infectious agent?

The correct answer is allergens, as they are not classified as infectious agents. Infectious agents are microorganisms that can cause disease, including bacteria, fungi, and viruses. Each of these types of agents can replicate and transmit infections to hosts, leading to illness.

In contrast, allergens are substances that can provoke an allergic reaction in susceptible individuals but do not cause infections. These substances can include pollen, molds, pet dander, or certain foods. Unlike infectious agents which have the capability to invade and replicate within a host, allergens trigger an immune response without being infectious themselves. Understanding the differences between these agents is essential in fields like healthcare and physical therapy, where knowledge of infection control and patient management is critical.