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

Pre-exposure prophylaxis, or PrEP, medications can also greatly reduce one's risk of contracting HIV in the first place. — Charles Trepany, USA Today, 2 July 2026

Rabies is almost always fatal in humans if not treated quickly with postexposure prophylaxis, or PEP. — Anders Hagstrom, FOXNews.com, 2 July 2026

But given that the boy already had rabies symptoms and that post-exposure prophylaxis actually can be harmful once symptoms set in, it was decided not to use PEP. — Theresa Gaffney, STAT, 29 June 2026

The number of people who received pre-exposure prophylaxis (PrEP) medication, used to prevent those at risk from contracting HIV, declined by a drastic 38 percent between 2024 and 2025, per initial data from 62 countries — which means more than a million fewer people took the drug. — Rael Ombuor, Washington Post, 13 June 2026

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

• postexposure prophylaxis
• pre-exposure 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