Final answer:
The two main symptoms of a pyrogen reaction are fever and chills, which occur as the immune system responds to pyrogens by raising the body's temperature.
Step-by-step explanation:
The two main symptoms of a pyrogen reaction are fever and chills. Pyrogens are substances that can induce fever, which is one of the body's natural defenses against infection. When a pyrogen enters the body, the immune system responds by raising the body's temperature, which can lead to the symptom of fever. Chills often accompany fever as the body's temperature begins to rise. Other symptoms can include headaches, muscle pain, and fatigue, but fever and chills are the primary indicators of a pyrogenic reaction.