FLEAS!

[Deleted]

Food-grade diatomaceous earth is effective for treating your home for fleas. Vacuum often and empty the vacuum frequently. Wash all bedding and linens the dog touches with hot water. Fleas tend to be more dormant in colder weather, but I don't know how cold it will be in your area.

Trifexis is another popular oral flea and heartworm medication. It may be worth a try? I'm not sure if it would work better than Comfortis.

[cmeon]

Do you/he actually see fleas? I mean, they aren't hard to miss with a flashlight and some patience. Fleas tend to hop from dog to dog in the same home, so I have a hard time believing that one dog is fine while the other is being eaten up (without you noticing the bugs).

Schnauzers are known for skin issues and allergies, they even have their own little thing coined Schnauzer Bumps. Environmental allergies can be a big problem for their skin, too. Just, before making any drastic changes- make sure you are actually dealing with fleas. Vets get it wrong sometimes, skin issues can be really tricky.

FWIW, Spinosad is the active ingredient in Comfortis, and also the "flea" portion of Trifexis. Advantage uses a different ingredient than Frontline's products, so if you actually are having a problem with fleas/Frontline products, I'd try one of the Advantage (or Bio-Spot) topicals first. Fleas in some regions react better to a specific chemical, sometimes.