It's cold outside. There's only so much clothes can do for an animal. Some dogs are bred to handle cold weather and naturally grow out their locks in winter for added insulation. They're so good at keeping warm that they don't mind swimming in near-freezing water. No matter what kind of ensemble you put together for your Chihuahua, he's not going to be comfortable in very cold conditions. Small, short-haired dogs have little insulation and a lot of surface area, so they lose heat rapidly. If a dog shivers furiously, then suddenly stops, he's in serious danger—it's time to get back inside immediately. Frostbite can also develop on the tips of the ears and tail. Sick, and older dogs may have thinning hair, which makes them particularly vulnerable to the elements.
Road salt can cause irritations to your pet's feet. Make sure you rinse the salt off after a walk on the roads where salt has been. Also be aware of ice balls that can collect between the toes of your pet, especially breeds that have a lot of hair between the toes. Road salt also contains a lot of impurities and is not safe to ingest.