Short answer
An infection involves an infectious agent growing in the body. Inflammation is the body’s response to injury or another trigger and may involve swelling, warmth, pain or immune activity. Infection can cause inflammation, but a sprained ankle or autoimmune condition can also be inflamed without a new infection. 1 2
Infection can trigger inflammation, but inflammation can occur without an infection.
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At a glance
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| Question | Infection | Inflammation |
|---|---|---|
| Primary process | Agent enters and multiplies | Body responds to a trigger |
| Requires a microbe? | Yes | No |
| Can happen together? | Yes | Yes |
The table summarizes the cited definitions and the article’s stated scope. 1 2
What each thing is
Infection. The establishment and multiplication of an infectious agent in a host. 1
Inflammation. A tissue and immune response to injury, infection or other triggers. 2
Key differences
The distinction separates cause from response. A pathogen can stimulate immune cells and inflammatory chemicals; those reactions may help control it but can also contribute to symptoms. Inflammation can also start after physical injury or persist when regulation fails, without an active infectious agent. 1 2
How to tell them apart
Ask whether there is evidence of an infectious agent and whether there is evidence of an inflammatory response. Redness alone does not prove bacterial infection; a positive microbial test does not by itself explain every inflamed area. A clinician interprets findings in context. 1 2
Where they overlap
Many infections produce inflammation, and an inflamed site may prompt investigation for infection. Both words can apply to the same tissue at the same time. 1 2
Edge cases
Some infections cause little visible inflammation, especially early or in a person with altered immunity. Chronic inflammation can continue after the original trigger has gone or begin without infection. The word “-itis” often signals inflammation, not necessarily infection. 1 2
Why the distinction exists
Medicine needs separate terms for an invading agent and the host’s reaction. The distinction prevents inappropriate assumptions about causes and treatments. 1 2
Common misconceptions
Inflammation is not proof that antibiotics are needed. Antibiotics target susceptible bacteria; they do not treat every inflammatory condition. 1 2
Examples
A cut infected by bacteria may be both infected and inflamed. A sterile ankle sprain can be inflamed without being infected. 1 2
Sources
Sources checked October 3, 2026.
- Centers for Disease Control and Prevention — Infection Control Basics. Overview and colonization.
- National Cancer Institute — Inflammation. Definition.