- List of biological barriers
- Blood-brain barrier, a biological barrier that prevents entry of harmful substances into the brain by selectively allowing some substances to pass through it
- Blood-testis barrier, the biological barrier between blood and testes
- Blood-placental barrier, the biological barrier between a pregnant person's blood and foetal blood (blood of the baby or babies)
- Blood-CSF barrier, the biological barrier between blood and cerebrospinal fluid (CSF; a.k.a. brain fluid)
- Blood–spinal cord barrier, the biological barrier between blood and the spinal cord