While human facial hair serves mainly as aesthetic expression, dog facial hair helps navigate the world. Dogs depend on these very sensitive whiskers for sensory information about objects close to the face. Dogs can and do lose whiskers, generally from disease or from groomers who remove the hair.
Grooming
Some groomers perceive dog whiskers as little more than overgrown facial hair, and may want to remove them during a pet groom. Unless you tell your groomer not to cut those hairs, you may end up with a dog who's missing her whiskers. Show dogs routinely have their whiskers clipped off for dog shows, for a "cleaner" appearance.
Cancer
One side effect of chemotherapy for dogs undergoing cancer treatment is whisker loss. If your dog experiences cancer-care whisker loss, the whiskers will grow back but may have a different texture. Dogs do not lose their fur during chemotherapy, since dog fur growth is seasonal and not constant, like human hair growth.
Other Causes
Skin infections can cause whisker loss in dogs. Dogs with demodetic mange, cause by a mite species, can experience facial hair loss. Symptoms include thinning hair, patchy hair loss and reddened or infected skin. Dogs who have alopecia may also lose whiskers. Alopecia may cause hair loss in patterns or varied locations, and may be accompanied by scaly skin.
Considerations
A dog can't focus well on objects close to her face, and her muzzle may also block close objects from view. Whiskers help dogs sense these close objects. Since dogs depend on their whiskers for sensory information, they can seem more uncertain in low-light situations without whiskers. They may move slowly, because they're not sure where obstacles are. Dogs who have poor eyesight particularly need whiskers for navigation.
