Diarrhoea is a symptom — frequent loose stools, from many possible causes. Dysentery is a specific kind of infection that causes diarrhoea containing blood or mucus, along with cramps and fever. All dysentery involves diarrhoea; almost no diarrhoea is dysentery.
The core difference
- diarrhoea — a symptom: loose, watery stools passed more often than usual.
- dysentery — an intestinal infection producing diarrhoea with blood or mucus in it, usually with cramping and fever.
Symptom versus disease
This is the whole distinction. Diarrhoea describes what is happening and says nothing about why — it can follow a virus, a change of diet, anxiety, a medication or a chronic condition. Dysentery names a cause: an infection invading the intestinal lining, which is why blood appears.
The two main types
- Bacillary dysentery — caused by bacteria, most often Shigella. The more common form.
- Amoebic dysentery — caused by the parasite Entamoeba histolytica, more associated with tropical regions.
Why it mattered historically
Before modern sanitation, dysentery killed on a scale that is easy to underestimate. It was a defining feature of siege warfare and long campaigns, and in several conflicts it caused more deaths than combat. The link to contaminated water is the reason sanitation infrastructure changed mortality so sharply.
The spelling
Diarrhoea is the British spelling; diarrhea the American. Both come from Greek dia- (through) and rhein (to flow). Dysentery is Greek too: dys- (bad) plus enteron (intestine) — literally bad bowels.
This page explains the words, not your symptoms. Blood in stool is a reason to see a doctor.
