Woody, a 4 year old male Border Terrier who developed sore lips for an unknown reason.

When Danielle came back from school, she could see that there was something wrong with Woody. When the small dog looked up at her, it was as if someone had put lipstick on him. His upper and lower lips were a bright pink colour, and when she looked closer, she could see that the skin in this area was reddened and swollen. Woody did not like Danielle paying close attention to his mouth. He wriggled and darted away, then began to paw at his mouth, rubbing the sore area with his front feet.

Danielle brought Woody up to see me that evening, and after examining him carefully, I asked a series of questions about his recent lifestyle. Was there anything new in his environment? Border Terriers are curious, intelligent dogs.  If there is something different or interesting in their surroundings, they are very likely to investigate it to find out more.  Since dogs have no hands to pick things up, they have to use their mouths. This means that if something irritant or toxic attracts a dog’s attention, their mouth is likely to be the most “at risk” part of their body.

Danielle explained that there was quite a lot going on at home. Builders had been constructing a conservatory, and although Woody had been kept away from their work area, there had been a lot of dust from plaster and cement in the air. At the same time, Danielle’s family had been painting another part of the house, so there had been wet paint in the area where Woody lived. None of these activities sounded as if they could cause Woody’s problem. Dust from modern building materials is relatively non-irritant unless an animal has direct contact with the source of the dust, which Woody could not have done. If he had tried to lick an area that was freshly painted, we would have seen the paint itself on his fur. So it seemed as if the home refurbishment was not to blame.

I then asked about Woody’s access to the garden. It turned out that he was able to run around the garden as much as he wanted, but there were no toxic or irritant plants. If he had chewed a plant such as Hogwort that contains caustic substances, he could suffer burns to his mouth. However, there was nothing new in the garden, no overgrown wild areas, and it did not seem likely that this was the source of the problem.

My discussion with Danielle had not come up with any obvious cause of Woody’s sore mouth. I decided to give him a simple treatment, with some anti-inflammatory medication and antibiotics. Often a dog may have a one-off encounter with an irritant, and the damaged skin can become infected and itchy. As a result, the dog rubs and scratches the affected area, perpetuating the redness and soreness. Often a general approach is effective, with a short course of treatment to help everything return to normal

Woody came back three days later, and although his lips looked a little less red, the problem had not gone away. This time, I had a longer discussion with Danielle and her family. We knew that something was causing Woody’s mouth to become red and sore, and we were sure that there was no obvious cause in his environment. At this stage, we had to start looking at the less common causes of the problem.

Food allergy can sometimes cause itchy skin, and this can sometimes be focussed around the lips, where the food has the most direct contact with the dog.  It is difficult to diagnose food allergy, and the only effective method is by putting a dog onto a standard, low-allergen diet. If Woody did not start to get better soon, this would be necessary.

Another rare cause of sore lips is a problem known as “auto-immune skin disease”.  For reasons that we do not understand, a dog’s immune system sometimes start to react against the dog’s own body. In the same way as a recipient of an organ donation can “reject” the new organ, a dog with auto-immune disease can start to reject its own skin. The result can be red, ulcerated areas, especially around the lips and eyes, and under the tail. Woody only had sore areas around his lips, so this was not a likely diagnosis, but it was definitely on the list of possibilities. A biopsy of the affected lip would need to be taken to look into this, and that would require a general anaesthetic and some minor surgery. Again, we decided that if Woody still had sore lips in a few weeks’ time, this would be on the agenda.

Woody is not at all bothered by his red lips – he is as care-free and cheerful as ever. After discussing the different options, Danielle and her family decided to go with a continued general treatment for a few weeks. Woody is on standard medication for infected, sore skin, with a soothing ointment, antibiotics and some antihistamines to ease any itchiness. He is not rubbing his mouth as much as he was, and we are hoping that this general approach will sort out the problem.

If Woody still looks as if he is wearing lipstick in 2 or 3 weeks, then it will be time for phase two, with special diets and biopsies. Watch this space!


  • Dogs investigate the world with their mouths
  • Owners need to be careful to keep all irritant substances out of pets’ reach
  • There are many causes of sore lips in dogs, and a precise diagnosis can be elusive

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Please note that I am unable to answer veterinary questions in comments. If you have questions or concerns about your pet's health it is always better to contact your vet.

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