Lip injections are a form of dermal filler
and work the same way.
Lip fillers are made with Hyaluronic Acid
(HA), a sugar that your body produces naturally. But as we age, our bodies produce less HA. Lip injections add plumpness by supplementing the naturally declining HA volume in your lips.
Additionally, hyaluronic acid is a humectant
: it attracts and holds water. So, HA lip injections draw water to your lips. This contributes to the increase in volume and helps keep your lips moisturized.