Why does my 3-year-old dog have wart-like bumps on her chin?

Hello. This is probably a case of chin furunculosis, a deep pyoderma or skin infection that can be from many causes, including food sensitivities. It often clears up with a round of antibiotics, & sometimes steroids, but may come back if the underlying allergen is not identified. I would start out by slowly switching her food to one indicated for skin issues. Both Purina Pro Plan & Hill's Science Diet have over the counter foods directed at dogs with sensitive skin & stomach issues. You can also clean the skin using a
benzoyl peroxide based soap or one with chlorhexidine ( Hibiclens - available at all pharmacies ). If this does not work, or you want to see quicker results, talk to your vet about oral antibiotic therapy, topical therapy with Mupiricin & a prescription hypoallergenic diet. Also, make sure all food & water dishes are either ceramic or stainless steel, no plastics. Hope the skin looks better soon & thanks for using Petco Pet Education Center, formerly Petcoach.