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-​ \

Definition of prophylaxis

: measures designed to preserve health (as of an individual or of society) and prevent the spread of disease

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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 The antibody therapy made by Regneron is also authorized to be used as a preventative treatment, or what's known as a post-exposure prophylaxis. Jen Christensen, CNN, 18 Aug. 2021 Pre-exposure prophylaxis — which includes the drugs Truvada, its generic counterparts and Descovy — are all incredibly effective at preventing HIV/AIDS infection. Ryan Kost, San Francisco Chronicle, 13 Aug. 2021 Woodhouse added that guests who were at the zoo during the day shouldn't be concerned since bats are nocturnal, but the guests who stayed overnight recently should get rabies postexposure prophylaxis (PEP), which will be paid for by the zoo. Paul Best, Fox News, 11 July 2021 The drug continues to be tested as possible prophylaxis against Covid-19 in other trials, the company noted. Siladitya Ray, Forbes, 15 June 2021 Prescriptions of PrEP, a preexposure prophylaxis that can prevent HIV infection, have also fallen sharply, according to new research presented at a conference last month. al, 22 Apr. 2021 Treatment for humans who may have been exposed to rabies is highly effective and involves a series of injections given over three to four weeks, called post-exposure prophylaxis. Annie Berman, Anchorage Daily News, 21 Apr. 2021 The pandemic has also impacted the distribution of preexposure prophylaxis, or PrEP, a once-daily pill used to prevent HIV. Dr. Tarun Jain, ABC News, 11 Mar. 2021 Antibody therapy was also a mainstay of infectious disease treatment before World War II, and still has some niche uses especially in post-exposure prophylaxis for several viral diseases. Arturo Casadevall, STAT, 4 Mar. 2021

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'prophylaxis.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

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First Known Use of prophylaxis

1683, in the meaning defined above

History and Etymology for prophylaxis

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

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Time Traveler for prophylaxis

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The first known use of prophylaxis was in 1683

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Last Updated

30 Aug 2021

Cite this Entry

“Prophylaxis.” Dictionary, Merriam-Webster, Accessed 21 Sep. 2021.

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More Definitions for prophylaxis


pro·​phy·​lax·​is | \ -ˈlak-səs How to pronounce prophylaxis (audio) \
plural prophylaxes\ -​ˈlak-​ˌsēz How to pronounce prophylaxis (audio) \

Medical Definition of prophylaxis

: 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

Britannica English: Translation of prophylaxis for Arabic Speakers Encyclopedia article about prophylaxis


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