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The Effect of Sun Exposure on Animals

Nov 2, 2023

It is well recognized in humans that excessive sun exposure increases the risk of many dermatologic conditions. While skin cancers are by far the most commonly recognized, other dermatologic diseases such as actinic keratosis, solar dermatitis, and even simple sunburns are also of significant concerns in human medicine. Less often considered is the effect of the sun on dogs and cats, who may also develop or decompensate diseases due to increased ultraviolet light exposure.

Animals possess natural protection from the sun's rays beyond what humans do. Their hair coat physically blocks out ultra-violet light, especially if the coat is darker in color. Many animals also have heavily pigmented skin (i.e. darker colored skin) with an abundance of melanocytes, the cells that help to protect the skin from the sun's damaging rays. Unlike humans, dogs and cats attain Vitamin D almost exclusively from their diet and so do not require ultraviolet light exposure to help synthesize it. Animals are generally at higher risk of sunlight associated diseases if their coats are thinner or they are hairless (ie Sphinx and Rex breed cats, Chinese Crested and Mexican Hairless dogs). Animals with white haircoats are also predisposed to these conditions. Certain areas on animals with less thick fur such as ears and the bridge of the nose are also commonly affected by sun related diseases.

The sun's ultraviolet radiation can cause a number of skin problems in pets. Sunburn can occur in dogs and cats, and presents similarly to humans, with red, peeling inflammation of the affected skin. Certain breeds of dogs (such as Dalmatians and Bull Terriers) and white cats are highly susceptible. Pets that have been recently groomed have a thinner and less protective hair coat and are, therefore, more likely to be burned. Repeated sunburns increase the risk of skin cancer significantly.

Diseases associated with sun exposure also include skin cancers- a classic disease of white cats in areas with heavy sun exposure is Squamous Cell Carcinoma on the tips of the ears. Cancers of the muzzle in dogs may also be related to sun exposure in some cases. Other, non-cancerous conditions may be triggered by exposure to sunlight; for example, some forms of the autoimmune diseases discoid lupus and pemphigus may be related to or triggered by sun exposure, as may the eye and skin disease “Vogt-Koyanagi-Harada disease”.

Avoiding sun associated disease is easier in Canada than in other geographic areas due to the less severe sun exposure seen at higher latitudes. However, the less common risk of sun associated disease also means that people may forget to take precautions when travelling or on hot summer days. These precautions may be quite basic and include keeping animals indoors or in shaded areas during the hottest portions of the day (which may also reduce the risk of heat stroke). If practical, application of sunscreen to exposed, pale, or thin-furred areas may be helpful; but ensure the sunscreen used is safe for pets (who may lick it off and ingest it).

References

  1. Dorn CR, Taylor DO, Schneider R. Sunlight exposure and risk of developing cutaneous and oral squamous cell carcinomas in white cats. J Natl Cancer Inst. 1971 May;46(5):1073-8. PMID: 5157843.
  2. Breen PT. Nasal solar dermatitis. Vet Med Small Anim Clin. 1972 Jun;67(6):652-3. PMID: 4483141.
  3. Egbeto IA, Garelli CJ, Piedra-Mora C, Wong NB, David CN, Robinson NA, Richmond JM. Case Series: Gene Expression Analysis in Canine Vogt-Koyanagi-Harada/Uveodermatologic Syndrome and Vitiligo Reveals Conserved Immunopathogenesis Pathways Between Dog and Human Autoimmune Pigmentary Disorders. Front Immunol. 2020 Dec 15;11:590558. doi: 10.3389/fimmu.2020.590558. PMID: 33384688; PMCID: PMC7770226.

Author

Matthew Kornya, BSc, DVM, ABVP (Feline) Residency Trained, Resident ACVIM (SAIM)
Consulting Editor