prophylaxis

noun

pro·​phy·​lax·​is ˌprō-fə-ˈlak-səs How to pronounce prophylaxis (audio)
 also  ˌprä-
plural prophylaxes ˌprō-fə-ˈlak-ˌsēz How to pronounce prophylaxis (audio)
 also  ˌprä-
: measures designed to preserve health (as of an individual or of society) and prevent the spread of disease

Did you know?

In Greek, phylax means "guard", so prophylactic measures guard against disease by taking action ahead of time. Thus, for example, before the polio vaccine became available, prophylaxis against polio included avoiding crowds and public swimming pools. These days a well-known kind of prophylactic is used to prevent sexually transmitted diseases; but prophylactic measures only work when people use them.

Examples of prophylaxis in a Sentence

Recent Examples on the Web
Examples are automatically compiled from online sources to show current usage. Read More Opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback.
For nearly twelve years, Gilead had been selling a pill named Truvada as a preventive treatment called pre-exposure prophylaxis, or PrEP. Jon Cohen, New Yorker, 24 June 2025 This method of receiving antibiotics after exposure, known as post-exposure prophylaxis, can help reduce their chance of contracting pertussis. Katia Hetter, CNN Money, 1 May 2025 The study provides aggressive case management to help patients navigate the health care system and stay on the treatment, known as pre-exposure prophylaxis or PrEP, which is available in both oral and injectable forms. ProPublica, 12 June 2025 That regimen, known as pre-exposure prophylaxis, or PrEP, is credited with helping beat back the disease in young people. Benjamin Mueller, New York Times, 4 May 2025 See All Example Sentences for prophylaxis

Word History

Etymology

borrowed from New Latin, from Greek prophylak-, stem of prophylássein "to keep guard before a place, be on guard, (middle voice) to be on one's guard against, take precautions against" (from pro- pro- entry 1 + phylássein "to keep watch on, guard, preserve," derivative of phylak-, phýlax "guard, guardian, protector") + -sis -sis — more at phylactery

First Known Use

1683, in the meaning defined above

Time Traveler
The first known use of prophylaxis was in 1683

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Cite this Entry

“Prophylaxis.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/prophylaxis. Accessed 4 Jul. 2025.

Medical Definition

prophylaxis

noun
pro·​phy·​lax·​is -ˈlak-səs How to pronounce prophylaxis (audio)
plural prophylaxes -ˈlak-ˌsēz How to pronounce prophylaxis (audio)
: measures designed to preserve health and prevent the spread of disease : protective or preventive treatment
prophylaxis against viral diseases
a paste containing fluorine for dental prophylaxis

More from Merriam-Webster on prophylaxis

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