Sunlight has been known as a wonderful disinfectant for more than a century, although its use as such has diminished. As long ago as 1877, two scientists, Arthur Downes and Thomas Blunt, discovered that sunlight was bactericidal. And, in 1890, the German microbiologist Robert Koch (who had isolated and described the tuberculosis bacterium in 1882), showed that sunlight killed TB bacteria.[i] Even further back in history, the legendary humanitarian Florence Nightingale observed that sunlight helped heal wounded soldiers and insisted that hospitals be constructed to allow the free entry of sunlight.[ii] In the 1860s, she stated five essential points in securing health in houses: pure air; pure water; efficient drainage; cleanliness; and light—especially sunlight.[iii] One can only wish that her recommendations were followed today, as it would save innumerable lives.
Sunlight as a disinfectant is making somewhat of a comeback, after being dropped in favor of harsh chemicals and antibiotics. While visiting in Mexico, a friend invited me to tour a bottled-water plant in a town called Juchipila. The water was exposed to ultraviolet light as a means of purification and it must have worked, because I drank it during my visit without ill effects. In a previous trip, I had made the mistake of drinking tap water at a restaurant and had paid a very dear price, commonly known as “Montezuma’s revenge.”
I also find it interesting that the Sonicare electric-toothbrush company now sells a sanitizer based on UV. The brush, after use, is placed in the UV sanitizer, and the company claims that it kills millions of germs in 10 minutes.
There are many other examples of the disinfectant power of the sun, but the latest has to do with disinfecting socks that have been contaminated with the virus that causes tinea pedis, a chronic skin disease. The objective of the research was “to evaluate the effectivity (sic) of sun exposure in reducing fungal contamination in used clothing.” Fifty-two socks, proven by fungal culture to be contaminated by patients with tinea pedis, were studied. The samples were divided into two groups: group A underwent sun exposure for 3 consecutive days and group B remained indoors. At the end of each day fungal cultures of the samples were performed.[iv] The researchers reported that elimination of the viral cultures was significant in the sun-exposure group, but not the indoor group.
This research took me back to my childhood, as I remember how fresh the clothing (including the socks) smelled after my mother had laundered it and hung it outside in full sunshine to dry. I expect than any fungi or bacteria were eliminated, along with the resultant odor that would have occurred if the clothing had been allowed to stay inside in a dark place.
So, if you want to disinfect your surroundings, try exposing them to sunlight whenever possible.
And, if you are the type of person who can immediately empty a crowded room by taking your shoes off, please hang your socks outside in the sun and air out your shoes before attending any public gathering. Florence Nightingale would be proud!
[i] Hobday, R. The Healing sun. Findhorn Press 1999:132.
[ii] Nightingale, F. Notes on Hospitals (third edition) Longman, Roberts and Green 1863
[iii] Hobday, R. Designing Houses for Health – A review. June 2010. Accessed 3/10/15.
[iv] Amichai B, Grunwald M, Davidovici B, Shemer A. Sunlight as a disinfectant. Isr Med Assoc J. 2014 Jul;16(7):431-3.