Inflammation
The body's protective response to injury, infection or irritation.
What it means
Inflammation is the body's response to injury, infection or irritation, classically described by four signs: redness, heat, swelling and pain.
Blood vessels dilate and become leaky, delivering immune cells and fluid to the affected area. It is a protective process, and a necessary one for healing.
The distinction that matters clinically is duration. Acute inflammation is brief and beneficial. Chronic inflammation persists and becomes damaging, driving conditions such as rheumatoid arthritis, inflammatory bowel disease and atherosclerosis.
Inflammation is not the same as infection. Infection is one cause of inflammation; most inflammatory conditions are not infections.
In practice
Why it matters
Because most inflammation is not infective, antibiotics are ineffective for the majority of -itis conditions.
Anti-inflammatory medicines suppress the response rather than treating its cause, and in some conditions — tendinopathy notably — the process is degenerative rather than inflammatory, so they help less than expected.
Clinically reviewed by Dr Mohammad Zubair Khan, GMC 7563469
Last reviewed
August 30, 2026