Fever in Adults

Common Causes

• Viral infections like flu or COVID-19 — Research suggests viruses may trigger fever as the body ramps up its defense, common in otherwise healthy adults (Mayo Clinic).
• Bacterial infections such as urinary tract infections (UTIs) or pneumonia — Bacteria might cause fever in adults, especially if the infection spreads or weakens immunity (CDC).
• Medications or vaccines — Some drugs or shots could lead to temporary fever as a side effect in adults (NIH).
• Autoimmune conditions like rheumatoid arthritis — Inflammation from these disorders may raise body temperature in some adults (Mayo Clinic).
• Cancers such as lymphoma — Certain tumors might cause persistent fever in adults, though this is less common (NIH).

Learn More

For a full overview of this symptom, including home remedies and when to see a doctor, read our complete guide on Fever.