Chemical burn from dentist

I recently went to the dentist to get a porcelain filling. As I was driving home, the novocaine began to wear off and I noticed a burning sensation on my upper lips and chin. When I looked in the mirror, I noticed a that I had a blister forming and that a white-ish powery crust had formed on my upper lip. It looked and felt like a chemical burn. When I tasted the "powder", it was very sour, like citric acid . When I got home, I washed off my face and a layer of skin came a way. I called my dentist and he said that it was an allergy to latex, or the white powder from the inside of his gloves. Can this be possible? It didn't seem like an allergic reaction, it really felt and looked like a localized chemical burn.