Why the first six hours tell you most
A tablespoon of mayonnaise is roughly the size of a cat’s stomach, so this amount will likely trigger either vomiting or rapid digestion. If she hasn’t thrown up within six hours, her system is probably handling it — but not out of the woods yet. High-fat meals can have delayed effects on cats, so the 12-24 hour window still matters.
Check her litter box for unusually soft or greasy-looking stools, which indicate her body is struggling to process the fat. The smell may be stronger than normal too, as mayo’s oils pass through. These signs alone don’t require a vet if she’s otherwise active and drinking water.
Position matters as much as symptoms
A cat in real distress will often hunch close to the ground with elbows tucked under, or press her belly against cool surfaces. These postures suggest abdominal pain beyond typical nausea. Time how long she holds these positions — more than 30 minutes of obvious discomfort warrants a call to the vet.
Notice whether she’s seeking isolation or still responsive to you. A mayo reaction alone shouldn’t make her withdraw completely. If she hides under furniture and ignores familiar cues like treat bags, something more serious could be developing.
The danger of second-day symptoms
Some cats seem fine initially only to crash 18-36 hours later when pancreatic inflammation builds. Key late warnings include refusing even favorite foods for two consecutive meals, or drooling while staring at water without drinking. These suggest nausea has escalated beyond simple stomach upset.
Gently feel along her left side behind the ribs — a tense or swollen area there could indicate pancreatitis. Compare it to her right side; they should feel equally soft. Any noticeable difference means she needs professional assessment, even if she isn’t vomiting anymore.
When to resume normal feeding
After a mayo incident, offer small portions of her regular food every 3-4 hours rather than free-feeding. This lets you monitor appetite accurately. If she keeps down four mini-meals in a row with normal energy levels, the crisis has likely passed.
Skip any high-treat foods for three days post-incident to give her system a reset. The exception would be using a dab of plain boiled chicken to test her interest in eating — but avoid mixing it with more mayo, even as a temptation.
The full verdict, portion guidance and serving notes are collected on the Mayonnaise food facts page.