Cats can be regarded as an important allergen source in dwellings. Sev
eral studies revealed the importance of cat allergens in allergic airw
ay diseases. Recent studies documented that only half of the cat aller
gic patients are cat holders actually or in the past, the other half o
f the cat allergic patients have never kept a cat. Cat allergen can be
found in areas without cat holding, too. Due to their physical charac
teristics cat allergens become airborne and can be carried off from th
e homes with cats into those without cats. The levels of cat allergens
to induce sensitization and clinical allergy are not yet determined.