Common, less-worrying reasons for skipped meals
Dogs sometimes skip a meal after a vaccination or other vet visit due to mild soreness or stress, during very hot weather when appetite naturally drops, after overindulging in treats or getting into something they shouldn't have, or simply from stress around a change in routine, travel, or a new pet in the household. Some dogs also become genuinely bored of the same food over time, especially if it's been unchanged for a long period, though this is less common than owners assume.
Signs that point to a medical cause
Appetite loss paired with vomiting, diarrhoea, lethargy, drooling, pawing at the mouth, weight loss, or a swollen abdomen suggests something more than pickiness. Dental pain, a cracked tooth, gum disease, or an abscess, is a surprisingly common and easy-to-miss cause of reduced eating, especially if your dog is still drinking water and interested in soft treats but avoiding hard kibble. Nausea from gastrointestinal upset, organ issues (like kidney or liver disease), or pain from an injury can all present primarily as "won't eat."
How long is too long to wait
A single skipped meal in an otherwise normal, active dog usually isn't an emergency. Not eating for more than 24 hours, or any reduced eating in a puppy, senior dog, or dog with an existing health condition, warrants a vet call sooner rather than later, since these groups have less reserve to cope with even short periods of inadequate nutrition. Complete refusal of food combined with any other symptom, vomiting, lethargy, pain, distended belly, should be treated as urgent, not something to monitor at home.
What you can check at home first
Look inside your dog's mouth for redness, swelling, broken teeth, or foreign objects if they'll allow it, check whether they're still drinking water normally, watch for any vomiting or changes in stool, and note whether they still show interest in extra-tempting foods like plain cooked chicken. This information is genuinely useful to share with your vet even if you end up needing a visit.
When to call the vet
If appetite loss lasts more than a day, is paired with other symptoms, or affects a puppy, senior, or dog with a known health condition, call your vet rather than waiting, describing exactly what you've observed (duration, other symptoms, any recent changes) helps them assess urgency over the phone and decide whether you need to come in same-day.
Try not to switch foods or add tempting extras in the middle of figuring out what's going on, since that can mask the original problem and make it harder for your vet to pin down the cause once you do get seen.