Is lip swelling considered allergic reaction?

Most likely: As i answered the question on tongue swelling there are several factors that cause swelling, allergic reactions being one. This needs to be evaluated by a board certified allergist.

It is possible.: It depends on the cause of the swelling. Create a diary - learn what precedes the swelling - whether it be food, a toothpaste, lipstick, etc - determine the trigger(s) and then assess.