Why do I get sick after running a marathon?
Last updated September 3, 2026.
Because 26.2 miles briefly rebalances immunity: a meta-analysis of 7 studies found an 18% higher rate of upper respiratory infections after marathons (OR 1.18), and studies of non-elite runners show the race dips salivary immune protection - the mouth and throat's antibody barrier. Exposure does the rest: start-corral crowding, travel, taper-week sleep disruption. The dip is real but small and temporary - days, not weeks. Pymander's escalation routing is built and tested specifically for this class of decision; see the safety architecture working paper.
What to do
- Sleep through taper week: the recovery lever with the best immune evidence.
- Protect days 1 to 5 post-race: real rest, not just reduced mileage - that is the window.
- Wash hands through race logistics: expo and travel days are the exposure peak.
- Get seen if: every hard effort brings an infection, or recovery takes weeks - that pattern is worth a check of iron, training load, and immune function.
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