The teachings of Islam emphasize the development of inner beauty and not prioritizing external physical appearance. Permanent physical changes, such as cosmetic improvements and interventions, are not allowed as they are considered to alter Allah's creation. This raises the question of whether lip fillers are allowed in Islam since they are non-surgical and temporary in nature, lasting up to about six months. It is important to remember that each person is different with their own unique characteristics and that even though you don't have the exact characteristics that are currently “ideal”, you're still beautiful.
However, the topic is often complex for Islamic patients because lip fillers are temporary and, therefore, the line between what is a permanent change in one's body and what is a short-term change in one's appearance is blurred. The rule applies if the swelling of the lips is permanent, however, if it is as mentioned in the question, that the effect is temporary and the lips return to their normal state, then there seems to be no objection as long as the means used are not harmful. Ultimately, it is up to each individual to perform their own ijtihad and come to their own conclusions about what is haram or halal. Trends like having big lips come and go, so it's important to remember that beauty comes from within.
