Hylenex is a concentrated synthetic form of an enzyme that naturally occurs in your body. When injected, it begins to break down hyaluronic acid, speeding up the dissolving process that would take place over time. The Hylenex is often mixed with lidocaine to improve comfort and leaves the area numb for about 30 minutes. The hyaluronic acid dissolves over the next 72 hours. If replacement of filler is desired, this can be performed in 2-4 weeks after, depending on the area.