How long does food poisoning take to start?
Last updated September 3, 2026.
Anywhere from 30 minutes to weeks - the germ sets the clock, and the CDC publishes the onset table. Staph toxins hit within 30 minutes to 8 hours, norovirus at 12 to 48 hours, salmonella at 6 hours to 6 days, and listeria can take one to four weeks. That range is why the last thing you ate is so often the wrong suspect. Symptoms last hours to days; bloody diarrhea, diarrhea over 3 days, fever above 102 F, uncontrolled vomiting, or dehydration signs are the see-a-doctor list.
What to do
- Map the clock backward. Fast vomiting after a meal points to toxins; next-day illness points to norovirus or salmonella.
- Hydrate in small sips. Oral rehydration beats big gulps that come back up.
- Skip anti-diarrheals for bloody stools or high fever. Those cases need a doctor first.
- Escalate the CDC list. Blood, 3-plus days, fever over 102 F, uncontrolled vomiting, dehydration.
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