I have had a history of being Algeria to cats. then one night the cutest ferrel kitten came over and decided to adopt my wife and myself. in the beginning he would come by and would not allow is to pet him but would allow us to feed him. After 5 minutes my eyes felt like someone was inserting tooth picks in them, with tears rolling down my face and burning feeling like a wildfire. We bought the Alen filters (actually 2) and today the kitten is very affectionate always rubbing against us....by the way no more tears or eye discomfort.