Hilary graduated from the Royal (Dick) School of Veterinary Studies in Edinburgh where she later returned to complete a residency in Veterinary Dermatology. Since then she has worked in Academia (the University of Bristol & North Carolina State University) and is now in private practice at the Dermatology Referral Service in Glasgow. She has specific interests in canine atopic dermatitis and adverse food reaction and is a member of the International Committee for Atopic Diseases in Animals.

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Dr. Marsella has received her DVM from the University of Milano, Italy in 1991. She has been a Diplomate of the American College of Veterinary Dermatology since 1996 and has been a UF faculty since 1997. She is a full Professor at the University of Florida and the director of the UF laboratory of Comparative dermatology. She is the past president of the American College of Veterinary Dermatology. 

She is a founding member of the International Task Force on Canine Atopic Dermatitis and has been co-Editor for Veterinary Dermatology and for the new BSAVA Dermatology Manual.  She has published more than 150 peer reviewed articles and numerous book chapters. Her research program has focused on the investigation of the pathogenesis of canine Atopic Dermatitis and the identification of novel treatments. She has validated a model of canine atopic dermatitis that reproduces the clinical and immunologic characteristics of both the human and canine disease. For this reasons, she has also been a Research Professor for 3 years in the College of Medicine, Dermatology Department working with MD dermatologists on comparative research projects. When not working, she is horseback riding in the woods on her Andalusians, swimming or enjoying Argentine tango.