Which of the following is a sign of infection?

• A. Fever
• B. Weight gain
• C. Muscle weakness
• D. Hair loss

Answer: (A)

Fever signals infection. When pathogens invade, immune cells release fever-producing substances called pyrogens that raise the brain’s set point for body temperature. This higher temperature helps curb microbial growth and enhances immune defenses, making fever a classic indicator of infection. The other options don’t reflect a specific response to infection: weight gain isn’t usually caused by active infection and can result from many factors; muscle weakness can occur during illness but isn’t a defining sign of infection; hair loss isn’t linked to acute infection.