Why a drop is different from a bite
That single drop of melted cheese is about the size of a pea once spread out on the floor. For a 15 kg dog, this amount is less than what they'd get from licking a butter knife clean. The lactose in such a tiny quantity won't overload their digestive enzymes, and the fat content is negligible at this scale. Even sensitive dogs usually handle these trace amounts without reacting.
What you're more likely to notice is your dog sniffing the spot for more cheese rather than any physical symptoms. The salt in that drop is too minimal to cause thirst, and the protein isn't enough to trigger pancreatitis. If he licks the floor obsessively afterward, it's the behavior that needs redirecting, not a medical concern.
When microscopic amounts matter
The only real risk from a drop would be if your dog had a known dairy allergy with previous anaphylactic reactions — but you'd already be carrying epinephrine in that case. For ordinary lactose intolerance, the threshold for symptoms is far higher. Think of it like a person with mild lactose intolerance tasting a spoonful of ice cream versus eating a whole bowl.
Watch his next meal for any hesitation to eat, as some dogs associate nausea with locations rather than foods. But with this exposure level, even that is unlikely. The main reason to remember this incident is to gauge his reaction if he finds cheese again, not because of health risks.
What not to do after minimal exposure
Resist the urge to give bread or other absorbent foods to 'soak up' the cheese — that actually increases the workload on his stomach. Don't withhold water thinking it'll dilute the dairy; hydration helps move the lactose through. Avoid giving anti-diarrheal meds preemptively; they're unnecessary for this exposure level and can cause constipation.
If you're used to hearing warnings about fatty foods, note that the danger comes from volume. That drop contains less fat than his regular kibble's coating. The stories about pancreatitis involve dogs stealing entire blocks or wheels of cheese, not floor remnants.
The one sign that would surprise me
In fifteen years of ER nursing, I've never seen a dog react to this little dairy. If yours vomits or has diarrhea after just a drop, it would point to either an extreme sensitivity (rare) or that he ate something else you didn't witness. True lactose intolerance builds with repeated exposure over hours, not from a single microscopic dose.
His weight puts this into perspective — that drop is about 0.01% of his daily calorie needs. For comparison, the lactose in his occasional dental chew probably exceeds what he just ingested. Monitor as you would after any minor dietary curiosity, but don't lose sleep over it.
The full verdict, portion guidance and serving notes are collected on the Cheese food facts page.