When i have to stop montelukast to my daughter , she developed swelling of face and eye burning ?

Allergies: She must have allergies! Over a 30 day period montelukast (singulair) inhibits "leukotrienes" which are chemicals active in the allergic process. As you stop taking the meds, it sounds like her allergies flared. Now I wouldn't say going off the med for one day would be a reason for them to flare. But if you missed it for a week and her allergies flared, that would make sense.