Why mould on soy sauce is less dangerous than it looks
While mould on most foods can produce toxins, soy sauce's high salt and acidity prevent harmful mould growth. The real concern remains the sodium content—those few licks still delivered a concentrated salt hit. Your cat's small size makes even this amount significant, especially since cats have low thirst drives and can't quickly flush out excess salt.
Watch for subtle changes like excessive grooming or a sudden interest in their water bowl. Tacky gums or skin that tents when gently pulled are dehydration red flags. Unlike dogs, cats rarely vomit from salt overload until it's severe, so don't wait for obvious signs. Offer multiple water sources—some cats prefer running taps or wide bowls to encourage drinking.
How the mould might still affect your cat
Though unlikely to be toxic, mould can irritate sensitive feline stomachs. If your cat starts vomiting or has diarrhoea within 6 hours, it's more likely from the mould's bitterness than poisoning. The vomit may contain specks of black or green from the mould particles—this isn't an emergency unless it persists beyond two episodes.
Check litter trays for unusually loose stools over the next day. Mould exposure sometimes causes temporary appetite loss—try warming their regular food to enhance the smell if they seem disinterested. Avoid offering new treats or foods, as this could mask whether symptoms are resolving.
The critical 12-hour window for salt monitoring
A 6-year-old cat's kidneys work harder than a kitten's, and salt stress shows gradually. In the next half day, note any behaviour changes like hiding more than usual or sitting hunched near water. These suggest nausea or headache from rising sodium levels—both are signs the body is struggling to balance fluids.
Measure water intake if possible. Normal cats drink about 60 ml per kg daily—drinking double that could mean salt-induced thirst. Weigh your cat tomorrow if you can; a 5% weight loss from dehydration warrants a vet visit. For now, wet food (even just the gravy) helps increase fluid intake without force-feeding water.
When mould becomes a secondary concern
Only if your cat develops respiratory symptoms—wheezing, sneezing fits, or watery eyes—should you suspect a mould allergy rather than salt effects. This is rare with incidental exposure but possible if they inhaled spores while licking. Allergic reactions typically appear within 1-3 hours, not days later.
Long-term mould ingestion risks don't apply here—your cat didn't eat enough for cumulative effects. Discard the contaminated sauce and wash the container with vinegar (cats dislike the smell, deterring future curiosity). Focus on salt management unless unusual symptoms emerge beyond mild stomach upset.
The full verdict, portion guidance and serving notes are collected on the Soy sauce food facts page.