The Mouse Grimace Scale: how to recognize pain on a mouse's face
A mouse in pain doesn't curl up or whimper the way a dog might: it often keeps behaving almost normally, while still giving away clues on its face. Find our daily care guidance in the rodent care and grooming section.
A scientifically validated grimace scale
Langford and a large team of researchers published the development of a facial-expression coding scale for pain in laboratory mice in the journal Nature Methods in 2010, now known as the Mouse Grimace Scale (research on Google Scholar). The team identified five facial features that vary reliably with pain intensity: narrowed eyes, a bulging nose, bulging cheeks, a distinct ear position, and whiskers flattened backward rather than held upright.
What an owner can watch for at home
Without aiming for a medical diagnosis, these cues help tell a mouse that's simply resting apart from one that's genuinely uncomfortable — a nuance that's hard to catch without knowing what to look for. Behavior is often the most misleading first clue, since a sick mouse frequently keeps eating and moving around almost normally until fairly late in the illness.
- Watch the eyes: prolonged narrowing, different from an ordinary blink, is worth taking seriously.
- Check ear and whisker position: ears pulled back and whiskers flattened, outside of sleep, deserve attention.
- Compare against the animal's usual state, by regularly watching your mouse when healthy so a change is easier to spot.
These facial signals add to other cues already known in the species, such as the ultrasonic vocalizations covered in our article on the fancy mouse's ultrasonic communication. If there's any lasting doubt about its health, our guide on transporting a pet mouse to the vet without stress covers how to plan the visit. Extra vigilance is also worth keeping for mammary tumors, covered in our article on mammary tumors in pet mice.
Frequently asked questions
Does this grimace scale replace a vet's opinion?
No, it only helps catch a warning sign earlier; any suspicion of pain or illness still needs an exotic-pet vet's assessment.
Is a mouse sleeping with half-closed eyes necessarily in pain?
No, this narrowing needs to be told apart from ordinary drowsiness; it's the sign persisting outside of sleep that should raise concern.
Do these signs apply to all rodents?
The scale was validated specifically in mice; comparable scales exist for other species, but the exact features differ. Find all our guides on the rodent hub.
This guide is part of Planète Pets’s Rodents universe. Our advice is general in nature: for any health concern, your veterinarian remains the only reference.