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Plain-language first, with specialist detail below. For understanding, not medical advice.

Long COVID Atlas › Glossary › Blood-brain barrier

Neurology

Blood-brain barrier

https://longcovidatlas.org/glossary/blood-brain-barrier

In plain language

What it is

The tight seal that normally keeps the bloodstream and the brain separated.

Why it matters

When it leaks, inflammatory signals reach the brain, which is linked to brain fog.

Think of it like

A border checkpoint that has started letting the wrong things through.

Why thinking feels slow bloodstream: lasting inflammation, clotting signals blood-brain barrier, now leaky microglia (brain immune cells) switch on brain fog: slow recall, poor focus,word-finding trouble
Brain fog is not laziness or anxiety. Lasting inflammation in the blood, together with a brain barrier that has become leaky, lets inflammatory signals reach brain tissue and switches on the brain's own immune cells, the microglia. That low-grade neuroinflammation is what slows recall, focus, and word-finding.

For specialists

Formal definition

A selective interface of brain endothelial cells with tight junctions; its disruption is measurable on dynamic contrast-enhanced MRI.

Mechanism

Endothelial injury opens the barrier, permitting immune and inflammatory crosstalk with brain tissue.

Sources

Related terms

NeuroinflammationEndothelial dysfunction