Many bacteria species live on the skin of dogs without creating any symptoms. Infection occurs when environmental factors allow germs to grow. A flea infestation, an allergic response, a wound, or an underlying condition that depletes the immune system might all be the cause. The most common symptom is a red or scaly patch on the dog's skin. Bacterial skin infections are common in puppies. The bacteria that normally inhabit the puppy's digestive system can move into the surrounding skin when the puppy's defense mechanisms aren't fully developed. These bacteria don't cause problems for most puppies, but they can spread to cause skin infections in older dogs or those with compromised immune systems. Dogs can get bacterial skin infections from contact with other animals or people. Pets that live in kennels or cages with other dogs or cats are at risk for these types of infections. If you adopt a dog from a shelter or rescue group, be sure to ask how they manage parasites. They might use products with chemicals known as demodectics (d-moe-deek-tics). These products kill the bacteria and other organisms that may be living on the animal's body. There are also safe ways to treat fleas and ticks that do not involve using pesticides. Your vet can tell you more about these methods. People can also get skin infections from dogs.