Such types of allergic reaction
may take place because of some injury to lip or allergy
to some food or allergy to some cosmetic or may be infection like herpes simples infection or sometimes as a part of some general medical condition.
Treatment at the moment is BENADRYL
or LORAYIDINE or CETRIZONE etc.
If the problem reocurs,then you have to consult a dermatologist
and try to find the offending agent or any other cause for a proper treatment.