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

This tipped the scientists off that there must be some molecule from the cancerous cells that can cross the blood-brain barrier and inflict good, not harm. —New Atlas, 29 Jan. 2026

Instead, within about 40 minutes of taking it, L-theanine crosses the blood-brain barrier and can help calm the nervous system, lowering heart rate and blood pressure. —Allison Forsyth, Health, 28 Jan. 2026

Cosmic radiation poses a series of risks, such as cognitive impairment and blood-brain barrier damage. —Chas Newkey-Burden, TheWeek, 21 Jan. 2026

If TNF‑α loosens the blood-brain barrier, inflammatory molecules from the blood – as well as disease-causing pathogens – may have increased access to the reward circuitry of the brain, potentially worsening neuronal damage and dysfunction over time. —Habibeh Khoshbouei, The Conversation, 9 Jan. 2026

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