Sunlight Is the Best Disinfectant

Louis Brandeis? Ralph Waldo Emerson? Robert Walter? Anonymous?

Dear Quote Investigator: There is a family of sayings about the effectiveness of light for the destruction of noxious infectious agents. This family also includes metaphorical instances in which corrupt behavior is revealed and blocked via publicity. Here are some examples:

  • Sunlight is the best disinfectant.
  • Sunshine is the best disinfectant.
  • The best moral disinfectant is publicity.

Would you please explore this topic?

Quote Investigator: In 1860 the well-known transcendentalist philosopher Ralph Waldo Emerson published a collection of essays on “The Conduct of Life” which included a piece titled “Worship”. Emerson employed an analogy equating the protective illumination provided by gas-light and the protective information provided by publicity. Boldface added to excerpts by QI: 1

As gas-light is found to be the best nocturnal police, so the universe protects itself by pitiless publicity.

In 1879 the journal “The Laws of Health” edited by Robert Walter published a short article without a byline about “Disinfectants” which included the following excerpt: 2

Sunlight is the best disinfectant. Malaria, for instance, which is one of the most difficult things to contend against, is dissipated when the sun shines, and exerts its pernicious influence at night.

The above statement was non-metaphorical. Many years later in 1913 lawyer Louis Brandeis penned a metaphorical instance that has become popular. The fame of Brandeis grew when he joined the Supreme Court of the United States in 1916. See further below for details of the 1913 citation.

Here are additional selected citations in chronological order.

Continue reading Sunlight Is the Best Disinfectant


  1. 1860, The Conduct of Life by Ralph Waldo Emerson, Chapter 6: Worship, Start Page 175, Quote Page 197, Smith, Elder and Company, London. (Google Books Full View) link
  2. 1879 January, The Laws of Health, Disinfectants, Quote Page 70, Column 3, Published by Robert Walter of Wernersville near Reading, Pennsylvania. (HathiTrust Full View) link