Why do lips swell and bruise?
Swelling with lip filler is very normal and to be expected. Most lip fillers are made from a substance called hyaluronic acid (HA) that looks the most natural in the lips. HA molecules exist in our bodies and are responsible for retaining water and making our skin look hydrated (among other things). Because they are water-loving molecules (hydrophilic), they tend to pull water into the tissue causing swelling. After a few days, the fluid starts to work it's way out as the tissue and filler balance together.  Another major reason for swelling and bruising is an injury to the tissue. This might sound scary but it's a normal physiological response to have swelling after an injury- like a needle puncture from a procedure.