blood-brain barrier

noun

ˈbləd-ˈbrān- 

: a naturally occurring barrier created by the modification of brain capillaries (as by reduction in fenestration and formation of tight cell-to-cell contacts) that prevents many substances from leaving the blood and crossing the capillary walls into the brain tissues

Examples of blood-brain barrier in a Sentence

Recent Examples on the Web

The brain is surrounded by a layer of tightly joined cells, called the blood-brain barrier, that acts as a bouncer turning away any substances deemed unworthy of accessing our most precious resource. —Matt Fuchs, Time, 2 Sep. 2025

The team developed a small, water-soluble molecule capable of crossing the blood-brain barrier called KDS12025. —Hannah Millington, MSNBC Newsweek, 22 Aug. 2025

But unlike newer allergy medications, Benadryl also crosses the blood-brain barrier and enters the central nervous system. —Emily Kay Votruba, EverydayHealth.com, 13 Aug. 2025

The biggest drawback, the outlet says, is that Benadryl crosses the blood-brain barrier — blocking the signal in the brain that causes an immune reaction to allergens like pollen or nuts. —Cara Lynn Shultz, People.com, 16 July 2025

Word History

First Known Use

1934, in the meaning defined above

Rhymes for blood-brain barrier

• noncarrier
• carrier

Medical Definition

blood-brain barrier

noun

: a naturally occurring barrier created by the modification of brain capillaries (as by reduction in fenestration and formation of tight cell-to-cell contacts) that prevents many substances from leaving the blood and crossing the capillary walls into the brain tissues

—abbreviation BBB