Hyaluronic acid filler is a substance your bady naturally produces to keep your skin plump and hydrated. As we age, we lose our volume and produce less HA. This makes us look older. HA filler is used to recreate a more youthful and fresher look.Hyaluronic acid filler is a substance your bady naturally produces to keep your skin plump and hydrated. As we age, we lose our volume and produce less HA. This makes us look older. HA filler is used to recreate a more youthful and fresher look.