Zinc is toxic to dogs if ingested. I learned this when I was trying to find a sunblock for Murray's nose (he has discoid lupus and the sun causes the tissue to break down on his nose). I had to do a lot of research to come up with a product, developed by a vet, that didn't contain zinc. See article below:Oh brother, all the things I didn't know I was going to need to know about bassets when I agreed to foster. I am so glad I found this site.
My last dog was a beagle-basset cross and I learned more than I ever wanted to know about ear smells and ear cleaning!!! Thank heavens for zinc diaper cream.
Zinc Toxicity in Dogs and Cats
Pennies made since 1982, zinc oxide skin preparations such as Desitin, and galvanized metal such as nails and staples. Other sources include calamine lotion, suppositories, shampoos, zinc undecylenate (Desenex), sunblock containing zinc oxide, fertilizers, and paint.