What are common signs of an infection?

Swelling and pus drainage are classic signs of an infection. When the body detects an infection, it responds by increasing blood flow to the affected area, which can lead to swelling due to the accumulation of fluids and immune cells. Pus, a thick fluid that can contain dead cells, bacteria, and immune cells, typically indicates the presence of an infection, particularly in cases involving bacterial pathogens. These signs are part of the body's inflammatory response to fight off invading microorganisms, making them strong indicators of infection.

In contrast, while fever can be a sign of infection, weight gain is not typically associated with infection and might indicate other health issues. Similarly, rashes and irritation might occur for various reasons, including allergic reactions or irritations that are not necessarily infectious. Fatigue and headache can be symptoms of many conditions, not specifically indicative of an infection, which further distinguishes the correct answer in identifying common infection signs.