Most everyone has, at one time or another, inhaled helium. The resulting squeaky, high voice is amusing---but can helium inhalation be harmful? The simple answer to this question is that in low concentrations, inhaled only occasionally, helium is completely safe. It is an inert gas, meaning that it doesn't react chemically with the body, nor can it cause cancer or allergic reaction. There are some potentially harmful side effects of helium inhalation, however, which are related to overuse or misuse of the gas.
Oxygen Deprivation
The most likely harmful effect of helium inhalation is oxygen deprivation. The body's cells depend upon oxygen to survive--the brain, in particular, needs a constant supply of oxygen to remain functional and maintain consciousness--and inhaling pure helium instead of the mix of oxygen and nitrogen that makes up Earth's atmosphere deprives the cells of the oxygen they need. A single lungful of helium won't likely cause harm, for the same reason that a person can hold their breath for a minute or two with no ill effects. As soon as the helium is exhaled and a breath of air replaces it in the lungs, oxygen is provided to the body cells and no harm results. Problems arise, however, with multiple breaths of helium instead of air. Just as a person can't hold their breath indefinitely--at some point, they must either breathe or pass out--it's not possible to maintain consciousness if helium replaces air for a long period of time. It's easy for a person to know when to stop holding their breath--they start feeling very uncomfortable. This, according to the textbook "Human Physiology," is because sensors in the brain respond to increasing levels of the waste product carbon dioxide, which is normally exhaled. If a person is breathing normally, but is taking in helium instead of air with each breath, carbon dioxide is exhaled as usual and never builds up. There are no oxygen sensors in the brain, meaning that the body doesn't recognize the oxygen deprivation. It's possible to breathe helium to the point of passing out without ever feeling uncomfortable.
Lung Rupture
Most people inhale helium from a balloon, but it's also possible to breathe from a pressurized helium tank, such as those used to fill balloons. This mechanism of helium inhalation introduces another potential risk--that of a ruptured lung. The lungs are quite similar to balloons, in that they expand when filled with air, and if overfilled, can burst. In the "Journal of the Royal Society of Medicine," Doctors Mark Turner and Peter Benton report a case of lung rupture in a deep-sea diver, following the inhalation of pressurized air. Since helium tanks are at similar pressures, inhalation directly from a tank has the same potential for injury.
High-Pressure Nervous Syndrome
A final risk of helium inhalation is associated with long-term exposure to highly pressurized helium gas. A study reported in "Electroencephalography and Clinical Neurophysiology" indicates that significant pressurized helium exposure can result in high-pressure nervous syndrome, a combination of symptoms including altered brain waves and scattered, short-term unconscious episodes as well as tremors in the extremities. While the conditions necessary to produce high-pressure nervous syndrome are unlikely to result from normal, recreational helium use, this condition is relatively common in very deep-sea divers, who breathe a combination of helium and oxygen in pressurized tanks and who must be monitored for the development of symptoms.
References
- "Human Physiology;" Lauralee Sherwood, Ph.D.; 2004
- "Journal of the Royal Society of Medicine;" Three cases of pneumomediastinum-after labour, sneezing and compressed-air diving; Mark Turner, M.B., Peter Benton, M.B.; May 1998
- "Electroencephalography and Clinical Neurophysiology; "The high pressure nervous syndrome during a simulated oxygen-helium dive; P. Bennet, E. Towse; October 1971
