In his investigations into superstition in London at the time of the First World War, Edward Lovett discovered that all over the capital working-class people wore strings of blue beads around their necks (inside their clothes) as a prophylactic against bronchitis. He was told that these beads were put round the necks of young children, and never taken off for the rest of their lives, and that the custom extended all over the country. A note in The Hospital of 25 December 1909 (quoted by Opie and Tatem) and a letter in N&Q (160 (1931), 206) confirm Lovett's findings. There are previous examples of blue being worn as a cure or preventative, in the form of threads or ribbon, although most known examples refer to Scotland.
Lovett, 1925: 81–4;Opie and Tatem, 1989: 33;Black, 1883: 112–14.