My dog had that a few times. I think it can come from food too, or an ingrown whisker or hair. I used a warm compress 2-3 times a day, and kept the area very clean, by wiping his mouth after eating, and cleaned it with a dilute Betadine solution. It looked like it was improving and went away within a week or so. If it gets any bigger, you may want to involve your vet, also if it interferes with his eating/drinking, or if he's scratching at it. Plastic can cause chemicals to leech into the food and water. Stainless steel is best, ceramic with lead free glaze is good also. If you must have something fancy... look into bowl holders made to fit stainless steel bowls. I need to do that too, as mine dump the water bowl if it's been sitting too long.
