prophylaxis

noun

pro·​phy·​lax·​is ˌprō-fə-ˈlak-səs 

 also  ˌprä-

plural prophylaxes ˌprō-fə-ˈlak-ˌsēz 

 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

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

Post-exposure prophylaxis for rabies in those who have not been vaccinated includes wound-washing, a dose of human rabies immune globulin -- a medication containing antibodies against the rabies virus -- and a four-dose rabies vaccine. —Sony Salzman, ABC News, 27 Mar. 2025

Landmark studies in South Africa have, for example, shown that anti-HIV drugs taken by breastfeeding mothers reduce the risk of transmission to their babies and demonstrated the power of long-acting pre-exposure prophylaxis for HIV that was Science’s Breakthrough of the Year in 2024. —Byjon Cohen, science.org, 22 Mar. 2025

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

Phrases Containing prophylaxis

• post-exposure prophylaxis
• preexposure prophylaxis

Rhymes for prophylaxis

• chemotaxis
• epistaxis
• anaphylaxis
• axis
• praxis
• taxus
• chemoprophylaxis

Medical Definition

prophylaxis

noun

pro·​phy·​lax·​is -ˈlak-səs 

plural prophylaxes -ˈlak-ˌsēz 

: 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