Glossary
Hygiene hypothesis
David Strachan's 1989 suggestion that childhood infection carried by older siblings protects against hay fever. The label misled: what protects appears to be animals, siblings, farm dust and outdoor microbes.
Published Updated
Where this comes from
In the reference topic that owns this term
Reference topic 18, The Immune System's Education, states the mismatch as a card: what the system evolved to expect, what it gets instead, and what happens in the gap.
Mismatch card
- What it expects
Early years full of microbes from siblings, animals, soil, water and food, and early tastes of lifelong foods.
- What it gets
Small families, indoor lives, fewer animals and, until recently, advice to delay allergenic foods.
- What happens in the gap
Tolerance fails outward as allergy and inward as autoimmune disease, diagnosed in about one person in 10 in the UK over two decades.
What that chapter recommends
3 of the 5 graded recommendations in Reference topic 18, strongest evidence first. How the grades work.
Introduce peanut and well-cooked egg early, and keep them in the diet
StrongEvidence grade: Strong. Multiple randomized controlled trials, or consistent large cohort studies with a well-understood mechanism.Under the 2017 US guidance, babies with severe eczema, egg allergy or both start peanut-containing food "as early as 4 to 6 months of age," after a clinician has considered allergy testing.
Take antibiotics when needed, not just in case
StrongEvidence grade: Strong. Multiple randomized controlled trials, or consistent large cohort studies with a well-understood mechanism.About 30% of US outpatient antibiotic prescriptions are likely inappropriate. Never refuse or stop a prescribed antibiotic without a clinician's advice (Chapter 20).
Keep washing your hands, with plain soap
StrongEvidence grade: Strong. Multiple randomized controlled trials, or consistent large cohort studies with a well-understood mechanism.Handwashing prevents diarrheal illness. In 2016 the US Food and Drug Administration barred triclosan and 18 other antibacterial ingredients from consumer washes.
Related terms
The argument behind this term, its studies and its notes are in Reference topic 18 of the reference library. The book gives the practical version. Get the book.