Willan was educated at Sedbergh School, and received his M.D. at Edinburgh in 1780 From 1781 he practised medicine in Darlington and then moved to London in 1783 as physician to the new Carey Street Public Dispensary, where he remained until 1803 teaching alongside Thomas Bateman. He was elected a Fellow of the Royal Society in 1809.
Following the example of Carolus Linnaeus, Willan attempted a taxonomic classification of skin diseases, describing impetigo, lupus, psoriasis, sceloderma, ichthyosis, sycosis, and pemphigus. Willan's portrait was reproduced on the cover of the British Journal of Dermatology for many years. Willan and Bateman working together provided the world's first attempt to classify skin diseases from an anatomical standpoint.
In 1790, Willan received the Fothergill Gold Medal from the Medical Society of London for his classification of skin diseases. In the same year he published an account entitled "A Remarkable Case of Abstinence", which detailed the case of a young Englishman who died in 1786 after fasting for 78 days - one of the earliest accounts of eating disorders in males.
A copy of one of his works was translated into German and published in Breslau in 1799. The English version has been lost.
In 1798, Willan described the occupational disease psoriasis diffusa, which affects the hands and arms of bakers, and in 1799 first described the exanthematous rash of childhood known as erythema infectiosum.
- Fagge, C. Hilton. On Disease of the Skin by Ferdinand Hebra, N.D. The New Sydenham Society, London.
- Site to view online Delineations of Cutaneous Diseases: Exhibiting the Characteristic Appearances of the Principal Genera and Species Comprised in the Classification of the Late Dr. Willan; and Completing the Series of Engravings Begun by that Author by Thomas Bateman, London, 1817.
- Robert Willan, M D, Observations on the Sulphur-Water, at Croft, Near Darlington 
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