Al-Razi Separates Smallpox From Measles
A Persian physician writes the first clear clinical account distinguishing two diseases long confused as one
Quick facts
- Names
- Al-Razi; Latin Rhazes
- Dates
- c. 865-925 CE (variously given 846-930, 854-932)
- Key work
- On Smallpox and Measles
- Case histories preserved
- Over 1,000
What happened
Abu Bakr Muhammad ibn Zakariya al-Razi, known to Europeans as Rhazes, was one of the most influential physicians of the medieval Islamic world. Working in and around the Persian city of Rayy, near modern Tehran, he left behind over a thousand recorded case histories that document his working life as a clinician. In his treatise On Smallpox and Measles he differentiated between the two diseases for the first time, giving detailed clinical descriptions of each and suggesting treatments matched to the severity of the symptoms. This mattered because the two illnesses, which look superficially similar in their early rashes and fevers, had long been treated as a single condition. His birth and death years vary across sources; the most frequently cited dates are 865 to 925 CE.
Why it matters
Telling one disease from another by its clinical course is the foundation of differential diagnosis, and al-Razi's smallpox-and-measles treatise is one of the earliest surviving examples done well enough to guide treatment. His thousand-plus case histories also model a habit that would define good medicine, recording what actually happened to real patients rather than reasoning only from theory.
How we know
Al-Razi's medical writings, including On Smallpox and Measles and his large collection of case histories, survive in manuscript and translation and are studied by historians of medicine, who confirm both his clinical descriptions and the difficulty of pinning down his exact dates.
Sources
- Cureus (via PMC / U.S. National Library of Medicine). Abu Bakr Muhammad Ibn Zakariya Al-Razi (Rhazes) (865-925): The Founder of the First Psychiatric Ward · Peer-reviewed (author-declared)pmc.ncbi.nlm.nih.gov · Cited as a "journal" source (no stronger domain match). · Link is live and its text matches the event's key terms (Jul 2026)
- U.S. National Library of Medicine (Islamic Culture and the Medical Arts). Abu Bakr Muhammad ibn Zakariya' al-Razi (Rhazes) · Reputable sourcenlm.nih.gov · The domain "nlm.nih.gov" is on our Reputable source registry. · Link is live and its text matches the event's key terms (Jul 2026)
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