Is breathing pure oxygen bad for you? Human blood is designed to capture oxygen and safely bind it to a molecule known as hemoglobin. However, if you breathe in a high concentration of oxygen, it will overwhelm the blood, disrupting the central nervous system, damaging the lungs, heart and brain.

Breathing 100% oxygen is harmful for the lungs and the brain and will cause death under normal pressures.


Continuous exposure to oxygen under normal pressure leads to death , however exposure for limited amount of time or under low pressures delays death or damage to organs

The Earth's atmoshphere has around 22% oxygen.How much is the upper limit of % oxygen before it becomes harmful(death or damage to organs) to a human?

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    $\begingroup$ Oxygen is also harmful at 22%; like most poisons, there isn't some magic threshold at which harm begins, though you can define one and go from there. How would you like to define the threshold at which you will start calling it harmful? $\endgroup$
    – Bryan Krause
    Nov 18, 2023 at 14:03
  • $\begingroup$ @BryanKrause If it were harmful , wouldnt we be not able to live on? $\endgroup$
    – Root
    Nov 18, 2023 at 14:07
  • $\begingroup$ We can't live forever on it, over time it causes us heart and vascular disease, cancer, etc. In the shorter term, it contributes to us needing to constantly replace proteins and other cellular components. It also almost caused the extinction of all life on earth, before life had evolved to deal with it. en.m.wikipedia.org/wiki/Great_Oxidation_Event $\endgroup$
    – Bryan Krause
    Nov 18, 2023 at 14:16
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    $\begingroup$ We need proteins regardless of this to feed the muscles off.And if im not mistaken , cancer doesnt come out in every human. $\endgroup$
    – Root
    Nov 18, 2023 at 14:20
  • $\begingroup$ Muscles do not feed off protein typically, carbohydrates are the energy source. Protein is needed in diet for amino acids which build proteins, including in muscle. Cancer is sort of a chance game; things that cause cancer create more opportunities to "win" that game through damage to DNA, it is not deterministic. There is lots of DNA to potentially damage; cancer happens when the damage happens to occur in the right combination of places $\endgroup$
    – Bryan Krause
    Nov 18, 2023 at 14:24

1 Answer 1


Oxygen is always harmful. It's tearing apart your cells as we speak. That's actually what we like about it. It's really good at tearing apart food molecules to get at the juicy energy inside, but it will also tear apart other things in the process. Oxygen and the oxidizing effects of it are probably a major factor in aging. When it first appeared on the planet in any sort of concentration as a waste product of photosynthesis, it led to the world's first mass extinction event. Since then, animals have evolved to not only tolerate it, but require it. Doesn't mean it's not still tearing you up from the inside though. The concentrations present in the atmosphere are the concentrations our body has become adapted to cleaning up after. Unless you need higher concentrations for some medical reason, stick to atmospheric concentrations.

  • $\begingroup$ As I'm sure you know by now, this site likes objective answers that can be backed up by references. Please edit your answer with suitable references for your claims. $\endgroup$
    – bob1
    Dec 14, 2023 at 2:18

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