When a cat runs her arm along the side of her face, she is occupied a favorite pastimes. She is grooming. Her compulsion toward cleanliness may seem a bit obsessive, but the act is natural. Her fastidious grooming ritual does a lot more than clear kitty nibbles from her face.
Your cat is naturally flexibly and can use her rough tongue to lick most of her body clean as well as distribute the oils in her skin, but her tongue is not long enough to give her face a good cleaning without help. Instead, she will lick her paws or forearms and rub the moist limb along her face to clean. The process also smooths the fur and gives her that silky, well-kept look that you envy when your hair refuses to do anything but scare the neighbors.
A cat's saliva helps her maintain a constant temperature. In warm weather, a good tongue bath will her her cool down, and in the cold, it bonds to her fur to create a barrier against the cold. When she licks her arm and rubs her face, she may be uncomfortable and trying to regulate her body temperature. The act is natural and a lot easier on her than talking you into adjusting the thermostat just for her.
Your feline friend has scent glands along the side of her mouth. She may be using her paws to carry the scent from sides of her mouth to other parts of her body because you have recently bathe the scent off her or because she rubbed up against something that has a scent she does not like, such as a couch that you sprayed with fabric freshener, a dog or even you after you have sprayed on perfume.
While you might bite your fingernails when you are nervous, some cats will spend some time grooming when they are anxious. Think of it as your cat petting herself to calm down. Combine the soothing act with the comforting scent from her own glands, and she is taking care of her mental health in the best way she knows how. And afterward such an exhaustive cleaning, she will be ready for her second favorite pastime—napping.
If your kitty friend has an injury on her face or arm, she may lick the injury to clean it. Her saliva acts as an antiseptic. Even if the injury is something you cannot see, such as a sprain, the act of licking may sooth her. If she is injured, you can inspect her arm and face for scratches. If the injury is internal or nonvisible, such as a sprain, she may limp when she walks or react when you gently inspect her with your hands. Lethargy is another symptom of injury or illness. Always consult a veterinarian if you think your cat is not well.