John Farrar Soothill (20 August 1925 – 23 September 2004) was an English medical doctor. He began his career as a nephrologist and later became a paediatric immunologist at Great Ormond Street Hospital.

John Soothill was born in 1925 in Blackheath, London.^[1] His father was the chief medical officer in Norwich and his grandfather, William Edward Soothill, had been the first professor of sinology at Oxford University.^[2] He attended The Leys School, Cambridge, and in spite of his dyslexia went on to study medicine at Christ's College, Cambridge.^[3] He completed his national service in Germany, did his clinical training at Guy's Hospital and Lewisham Hospital.^[2] In 1955 he travelled to Chicago on a Fulbright Scholarship,^[3] where he studied the recently developed technique of renal biopsy.^[1] Soothill began working at Birmingham University's experimental pathology department in 1956 as a nephrologist. His work at Birmingham centred around kidney disease, immunoglobins and the complement system. He also pioneered the use of cyclophosphamide in children with relapsing nephrotic syndrome.^[2]

In 1965, Soothill moved from Birmingham to the UCL Great Ormond Street Institute of Child Health, where he was appointed the first Hugh Greenwood Professor of Immunology, a post he would hold for 20 years. One of his main achievements at Great Ormond Street was classifying the different subtypes of severe combined immunodeficiency (SCID).^[2] The disease, informally known as "boy in the bubble syndrome" after David Vetter, was given its current name by Soothill in the 1970s.^[1][4] He also focused on childhood allergies, proposing the theory that allergies and eczema resulted from the exposure to allergens in the first six months of a baby's life.^[2][3] He pioneered the use of elimination diets whereby a child with an unknown food allergy is denied all possible allergic sources in their diet, then each food is reintroduced one by one until the causative food is identified.^[1]

Soothill retired in 1985 to Devon with his wife Brenda Thornton, whom he had married in 1951. He died on 23 September 2004 in Axminster.^[1]