My bottom lip is bigger than my top lip what could cause that? (photo)

this is your genetics!  if you want this improved there are many cosmetic treatments such as fillers, fat injections, and implants.  Best, Dr. Emer.

Thank you for sharing your question and photograph.  In the majority of patients their lower lip is naturally larger than their top lip and patients can choose to augment one, or both, through the use of a hyaluronic acid dermal filler such as Juvederm.  See an ASPS board certified plastic surgeon in consultation to have the best recomendations made.