Why do cats shed their cat hair?
by KittyKondo.com 

     Outdoor cats normally shed their coat twice per year because of seasonal changes in relation to light and temperature. Indoor cats still shed but the cat hair will come off more gradually and throughout the year due to constantly stable indoor conditions. If you have a long-haired indoor cat brushing and grooming once a day is encouraged.

     Aside from the weather cats will shed automatically as a reaction to stress. Stress for a cat might include visiting the veterinarian, your long absence from the home, the new pet dog, etc. If kitty is nervous to a new or unexpected event he or she will cast off his cat hair.