Lip swelling in dogs is caused by many things including allergies, abscesses, dental problems, cancerous and noncancerous tumors, bites and bacterial infections, according to WebMD. Some dogs, such as Labradors and boxers, have a rare condition called craniomandibular osteopath that causes swelling of the jaw.
Allergic reactions to foods, bee stings, insect bites or certain medications can cause swelling of the face, including the lips, says WebMD. Abscesses, caused by dental problems, animal bites and other puncture wounds cause a swollen bulge to form at the affected location. Abscesses are dangerous to a dog's health and veterinary care is essential to prevent health complications due to infection. Tumors can also cause the lips to swell. Although tumors are not always cancerous, it is important to have the dog evaluated by a veterinarian to diagnose and treat the tumor.
Damaged or infected teeth can also cause the mouth and lips to swell, and require removal of the tooth or antibiotics, states WebMD. A bacterial infection called cellulitis, caused by bites or punctures to the skin, may also contribute to swelling. Because swelling of the lips or face can be life-threatening it is important to get the dog to a veterinarian as soon as possible.