Facial swelling can be due to an allergic response to any allergen which can be an inhalant, an ingestant or a contactant. To pinpoint a particular allergen is difficult. But since you've already observed it, best way to avoid another episode is to stay away from that allergen.
Next Steps
if the swelling is severe, kindly visit a doctor so that he/she can assess the extent of the allergic reaction. meanwhile you can take a levocetrizine plus montelukast preparation and visit the doctor immediately.