Why is it safe?
Hard and semi-hard cheeses contain significantly less lactose than milk because most lactose is expelled with whey and converted to lactic acid during production. Small amounts of plain hard cheese are generally tolerated by most cats and are not toxic. Cheese is high in fat and protein, not a concern in very small amounts, but excessive consumption contributes to weight gain.
Affected Systems
Digestive
Symptoms
Mild vomiting or soft stools in sensitive cats. Weight gain with habitual overfeeding.
What To Do
No action needed for small amounts. Monitor sensitive cats.
Notes
Never give: blue cheese (Penicillium molds produce roquefortine C, potentially neurotoxic in cats), cheese with added onion or garlic (toxic), flavored spreads or dips (often contain toxic additives). Plain hard cheese (cheddar, gouda, parmesan) in tiny amounts is safe and sometimes useful for concealing medication.
Sources
→ ASPCA Animal Poison Control Center — aspca.org
→ VCA Animal Hospitals — vcahospitals.com