Among the stranger bits of old folk traditions was the association of smallpox and the color red. It advised that the patient dress in red clothes, consume red food and drink, and exclude all light from the sickroom except red light.

The idea was supported by Niels Finsen, a Danish doctor who won the Nobel Prize in 1903, largely for his work on phototherapy, where he had particular success in treating the tuberculous skin ulcers of lupus vulgaris with concentrated light, probably because of its germicidal or heating activity. Like many discoverers of new ideas, he did not hesitate in applying the treatment widely and to find evidence for its application to other skin conditions, including smallpox.

Submitted by Ronald Fishman, from the Cogan Ophthalmic History Society