Hay fever was rare in early clinic notes and common in late-20th-century cities. That contrast invited theories.
Sanitation's century also emptied wards of cholera. Any honest history holds both graphs.
Timeline
John Snow maps cholera to a Soho pump — clean water as data, not fashion.
Jersey City's early municipal chlorination becomes a model for urban water.
Asthma and hay fever climb in many affluent countries as infections fall.
The hygiene hypothesis is named from family-size patterns in hay fever.
Alpine farm-child studies add livestock and stables to the exposure list.
Rook argues for co-evolved organisms rather than dirt as such.
Finnish and other work links surrounding biodiversity to atopic risk talk.
Texts warn against anti-hygiene readings while keeping the immune-training question open.
The timeline is intellectual history, not a lifestyle brand.
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