Photosensitization in Dogs

Photosensitization happens when the skin becomes overly susceptible to ultraviolet light due to the presence of photodynamic agents.  Skin that is lacking hair or pigmentation will be more sensitive to sunlight. Photosensitization differs from a sunburn, which causes skin changes without the presence of a photodynamic agent.

Photosensitization in dogs can lead to necrosis, skin ulcers and edema. The onset of clinical signs will depend on what type of photodynamic agent your pet was exposed to, the amount of the agent and the amount of the exposure to sunlight.

If you believe your dog has photosensitization, please make an appointment with a veterinarian. The stress, pain, and severe skin necrosis can become debilitating and may be fatal to your pet’s life.

Photosensitization occurs when the skin has a reaction to direct sunlight and becomes oversensitive. This condition is due to photosensitization, the build-up of photosensitive compounds under the skin.

• Hives appear after exposure to sunlight
• Dermatitis (inflammation of the skin) after exposure to sunlight
• Skin rash after exposure to light
• Canine scratches at muzzle or ears
• Skin scabs
• Canine may fidget, turn from the sunlight
• Discharge from the hives
• Necrosis (skin death)
• Skin ulcers
• Redness of the skin
• Edema (fluid retention)

• The dog ingests certain plants, fresh or dried – such as Buckwheat, Smartweed and St. John’s wort (Hypeicum perforatum)
• Buckwheat, Smartweed and St. John’s wort can also be absorbed through the skin
• Fungi
• Tetracycline, and some sulfonamides
• The photodynamic substance is phylloerythrin, a by-product of chlorophyll in the body
• Photosensitization has been associated with dogs that have liver damage due to poisons

The veterinarian will take a thorough medical history of your pet. It is a good idea to bring a list of any current medication or supplements your pet may be on. The veterinarian will ask you what symptoms you have seen in your pet and when they first started. Let the veterinarian know if your pet has recently been exposed to rat poison or any other toxic chemicals. 

He will perform a physical exam on your dog, which might include checking your dog’s vitals, taking a closer look at the dermatitis and palpation of the stomach area.

The veterinarian will probably run blood tests including a complete blood count (CBC) and a biochemistry panel. Blood work can help diagnose any underlying disease or toxins that may have triggered the photosensitization in your pet. If your veterinarian suspects that your pet has liver disease, he may recommend evaluating liver enzymes and performing a liver biopsy.

To help relieve your pet’s skin, your dog should not have direct contact with sunlight. He should be kept indoors as much as possible during the day and only walked in shady areas. You can investigate the option of  protective clothing for your pet. Because many pet owners are aware of the potential dangers or complications of too much sun for their dogs, the pet care market now has several good options available for sun protection. 

The veterinarian may prescribe corticosteroids if needed and in the case that there is a skin infection, your pet will need to be on antibiotics.  If there is any underlying disease that was diagnosed concurrent to the photosensitization, your veterinarian will discuss the appropriate treatment plan for your pet.

It is important to follow the treatment plan your veterinarian team has given you, for the wellness of your pet.  If you observed any other symptoms or if it appears the skin is getting worse, please call the veterinarian office.  Follow-ups visits will be necessary to monitor your pet’s progress. The skin lesions can heal well even after necrosis. The healing process will depend on the severity of the lesions, the presence of a bacterial infection and/or if there is an underlying disease.

Please be aware that the skin damage caused by photosensitization can attracts flies. Try to keep flies away from your pet, to avoid a maggot infestation on his skin.