How Long Can the Brain Survive Without Oxygen?

Stroke will not cause the brain cells to die immediately, but, the longer the lack of oxygen persists, the more severe the harm to the brain, according to the medical resource StatPearls. 

In as little as five minutes, low oxygen can cause coma, seizures and neuron death, according to the National Institute of Neurological Disorders and Stroke (NINDS).

Fortunately, people can still recover substantial brain function after a stroke if they are treated fast enough.

Complete lack of oxygen in the brain will cause the brain cells to die within "several minutes," Gonzalez said. In cardiac arrest, spontaneous electrical activity in the surface of the brain disappears within 10 to 30 seconds of the cessation of blood flow, according to a 2016 review of human and animal studies. 

Permanent brain damage can occur within just four minutes if a person's blood flow stops, according to the National Library of Medicine's MedlinePlus. 

"Any prolonged anoxic brain injury [caused by a complete lack of oxygen] that results in a large amount of cell death increases the risk of brain death diagnosis during hospitalization," Gonzalez said. 

Brain death, also known as "death by neurologic criteria," is the complete, irreversible loss of brain function.

Although brain damage from low oxygen generally occurs in a matter of minutes, the exact rate at which damage sets in can vary person to person. 

"It is certainly dependent on the individual and what risk factors one may have, such as blood pressure, cholesterol, and smoking," Gonzalez remarked. 

Poor cardiovascular health can lead to a buildup of fatty plaques that harden and narrow the blood vessels, which in turn limits blood flow to tissues and organs, including the brain. 

That said, poor cardiovascular health may sometimes offer an unlikely advantage in the case that the brain is deprived of oxygen.

"A person with a long standing history of risk factors can develop arteries or compensatory flow patterns to aid them when brain tissue begins to lose oxygen," Gonzalez stated.