Dear Dr. Fox:
In response to B.E. in Hendersonville, N.C.: Nothing was mentioned about the possibility that the cat experiencing hair loss might be allergic to its cat litter.
The same reaction happened to one of my cats. Given the location of the fur loss, I determined that my cat was reacting to the chemicals in various cat litters. After we switched to 100 percent clay cat litter, our cat improved, and her fur came back. B.E. might want to give this a try.
Many factors should be considered when a cat develops what appears to be an allergy that manifests itself as asthma or a loss of fur.
Hair loss might be on the flanks or legs, where the cat licks most, presumably because of feeling itchy all over. Inhaled allergens often trigger such behavior. More rarely, there is a reaction on the parts of the body that come into contact with the allergen, whether it's a wool blanket, a floor cleaner or an ingredient in cat litter. The paws and underbelly might be affected.
Clearly, your detective work paid off. I caution against clay-based litter because some are dusty and contain lung-harming microscopic particles of silica. At all costs, avoid scented and deodorizing chemical-laced litter materials.