Why only one cat needs monitoring
Since only your 6 kg cat ingested the sour cream, focus your attention there. Cats vary widely in lactose tolerance, and even a small amount like a dollop can trigger digestive upset in some individuals. The other cat, having consumed none, faces no risk from this incident. Their systems won't react to what they didn't eat, so you can set aside concern for them completely.
Watch for subtle changes in the affected cat's behavior—hesitation before jumping, less interest in play, or excessive grooming of the belly area. These often precede more obvious symptoms like vomiting or diarrhoea. The lack of shared symptoms between your cats confirms this isn't environmental and truly stems from that single lick.
What to expect in the next 12 hours
For a cat of this size, the dollop likely contained about a teaspoon's worth of sour cream—enough to matter but not enough for severe poisoning. Most reactions begin within 4-6 hours as the dairy moves through their system. You might hear stomach noises before any visible signs appear, especially if this cat doesn't normally consume dairy products.
Diarrhoea from lactose intolerance typically looks softer than usual but not watery, possibly with a slightly sour smell. Vomit may contain undigested food mixed with white froth. These symptoms usually peak within 8 hours and resolve by the 24-hour mark unless your cat has exceptional sensitivity.
When quiet observation beats intervention
For a one-time small exposure like this, withholding food for 4-6 hours often helps more than rushing to the vet. An empty stomach allows irritation to settle. Offer water frequently in small amounts—about two tablespoons every 30 minutes—to prevent dehydration without overwhelming their system.
Resist giving any human medications or home remedies, as cats process drugs very differently than we do. Even seemingly gentle options like pumpkin puree can backfire if your cat isn't used to fiber. The safest approach is letting their body handle this naturally while you monitor for worsening signs.
The tipping point for vet care
While most cats bounce back from dairy exposure on their own, contact your vet if you see multiple vomiting episodes (more than three in six hours), diarrhoea lasting beyond 24 hours, or refusal to drink water. A 6 kg cat has good reserves, but prolonged fluid loss changes the equation.
Also watch for lethargy that persists after their stomach should have emptied—about 8 hours post-licking. Normal tiredness from digestion differs from concerning weakness; if they can't or won't lift their head when you offer a favorite treat, that signals deeper trouble. Otherwise, this will likely pass without medical intervention.
The full verdict, portion guidance and serving notes are collected on the Sour cream food facts page.