What can increase a person's susceptibility to infection?

The option that indicates chronic illness or stress can increase a person's susceptibility to infection is accurate because both factors significantly compromise the immune system. Chronic illnesses, such as diabetes or autoimmune disorders, can impair the body's ability to fight off pathogens. Similarly, prolonged stress can lead to hormonal changes that may decrease immune function, making an individual more vulnerable to infections.

In contrast, regular exercise, strong immunity from vaccinations, good nutrition, and adequate rest are known to enhance overall health and fortify the immune response, making individuals less susceptible to infections. Thus, while chronic illness and stress weaken the immune defenses, the other options contribute positively to an individual’s ability to resist infections.