A lot of people may not think dog coats are necessary and are just useless fashion accessories, however this isn't truthfully the case. Some dogs lack the necessary body features in order to stay warm when it is cold, unsurprisingly most of these dogs are small breeds or dogs who usually have long fur but are cut short to avoid matting, so does your dog need clothing?
If you are still undecided, then think about this: Sure, dogs come equipped with their own external layering system, but some dogs have lighter layers of fur than others, and some are not genetically suited to the environments in which they find themselves transplanted. So your dog may in fact be extremely uncomfortable with the winter temperatures — as uncomfortable as you would be if you went outside without clothing.
A sweater or jacket can be helpful during the cold seasons, especially if your dog is reluctant to go outside in the bitter cold to do their business but how warm your dog is able to physically keep themselves may depend on his breed, size and even age, but if he just doesn’t have a heavy hair coat, there is only so much curling up he can do to conserve heat.
Smaller, light bodied breeds, toy breeds, and breeds that naturally have very short or thin hair coats benefit from a warm dog sweater for when they need to go outside, or for just hanging around the house. A sweater can make a significant difference in your dog’s feeling of well-being. Older dogs with weaker immune systems and dogs with diseases that impair hair growth typically need an extra source for warmth, and this can be easily provided by a sweater or jacket, even indoors.
On the other hand, larger dogs with dense hair coats will not need additional insulation, and could be very uncomfortable if they were forced to wear outer clothing, possibly causing them to overheat as their fur is already genetically designed to protect them from extreme winter temperatures. The Siberian Husky, Malamute, and Saint Bernard breeds are all excellent examples of dogs that are perfectly suited to cold temperatures, while the Chihuahua, Greyhound, and many terrier and pinscher breeds are good examples of dogs that would do well with a little extra outer insulation.