Azo dyes and the blood–brain barrier: Robert Aird’s novel concept in chronic neurological disease (1903–2000)

The well-established medical involvement of derivatives of the azo dye industry lent credibility to the 1935 announcement by Stanley Cobb of the use of vital brilliant red dye as an anticonvulsant. Although in the fullness of time clinical experience would discard this concept, nevertheless it was to give rise to Robert Aird who posited that the mechanism of action of this dye was due to its ability to decrease the permeability of the blood–brain barrier. In a very prolonged exploration of this concept, Aird concluded that blood–brain barrier permeability underlay the causation of a long list of chronic neurological conditions – a concept that was eventually abandoned. This article examines the details and the effects of this concept and its impact upon neurology.