RESUMO
INTRODUCTION: The use of hyaluronic acid (HA) as a dermal filler is considered safe. However, as new brands come to the market, reports of adverse events are becoming more and more common. OBJECTIVE: To describe a particular type of adverse effect that, unlike the erythematous, indurated, and painful nodules described in the literature as "angry red bumps," is characterized by noninflammatory, stony-like nodules that appear in sites previously treated with HA. METHODS: The report of four patients who presented this complication, and the occurrence of two HA syringes from the same batch that had hardened the product inside at the time of filling. CONCLUSION: The authors propose the nomenclature "happy bump" to group adverse reactions to HA that translate into noninflammatory nodules, with a stony consistency, appearing up to 4 weeks (recent) or after one month (late) in sites previously treated with AH.