Cats can spend more than half of their waking hours grooming themselves by licking their fur and paws, sharpening their nails and combing their paws through their fur. This grooming is not a simple act of boredom and narcissism, though: cats groom themselves for a variety of reasons, from removing the smell of their food to protect themselves from predators to regulating their body temperature through the cooling power of evaporating saliva. Cats' saliva not only acts as a stand-in for sweat, which cats mostly do not do, but also as a healing enzyme that can help wounds heal faster while staving off bacterial infection.
Because grooming is an important task into which most cats put a lot of time and effort, a cat that appears unkempt and poorly groomed may be sending a signal that he or she is sick or injured. This is particularly true if the cat in question normally looks salon fresh most of the time. However, though cats spend so much of their lives preening and cleaning, there is such thing as too much, and cats can become fixated on cleaning certain areas that will lead to bald patches where fur should be. This could be another sign that the cat in question is unhealthy.