What happens if oxygen levels increase?

October 2, 2025 •

4 min read

While oxygen is essential for survival, the human body has a narrow tolerance for an oversupply. When oxygen levels increase significantly, it can lead to a condition known as hyperoxia, causing damage to cells and tissues throughout the body and resulting in serious health complications.

Quick Summary

Excessively high oxygen levels can lead to oxygen toxicity, which causes damage to cells and tissues, particularly in the lungs and central nervous system. This condition can trigger a range of symptoms, including coughing, chest pain, vision changes, and seizures, especially in patients receiving supplemental oxygen or during hyperbaric therapy.

Key Points

High Oxygen Levels Lead to Hyperoxia: An excessive increase in oxygen can lead to hyperoxia, a condition where oxygen becomes toxic to the body.
Oxidative Stress Causes Cellular Damage: The root cause of oxygen toxicity is oxidative stress, a process that damages cell membranes, proteins, and DNA through reactive oxygen species.
Lungs and Brain Are Most Vulnerable: The lungs and central nervous system are particularly susceptible to damage from high oxygen, leading to pulmonary and neurological symptoms, respectively.
Toxicity Can Be Acute or Chronic: Symptoms can be acute (rapid onset, like seizures from hyperbaric therapy) or chronic (prolonged exposure, like lung damage from long-term ventilation).
Medical Supervision is Crucial: Oxygen therapy requires careful medical supervision to ensure levels are safe, especially in vulnerable patients like premature infants or those on ventilators.
Prevention is Key: Controlling oxygen concentration and exposure duration is the primary method of preventing oxygen toxicity in medical settings and during activities like diving.

The Dangers of Excess Oxygen: Understanding Hyperoxia

Oxygen is a life-sustaining gas, a cornerstone of aerobic respiration that powers our bodies. In fact, air in our atmosphere is only about 21% oxygen, a concentration that keeps our bodily functions in perfect balance. When oxygen levels in our blood and tissues increase above normal, a condition known as hyperoxia occurs. Unlike the beneficial effects of oxygen therapy for those with deficiency (hypoxia), excessive levels can be harmful, even toxic.

The Mechanisms Behind Oxygen Toxicity

The core of the problem with excessive oxygen lies in the formation of reactive oxygen species (ROS), which are unstable, highly reactive oxygen derivatives. While our bodies have natural antioxidant systems to manage normal levels of ROS, an oversupply of oxygen can overwhelm these defenses. This leads to oxidative stress, a process that can damage cell membranes, proteins, and DNA, much like iron rusting. This cellular damage is the root cause of oxygen toxicity and affects multiple organ systems, with the lungs and central nervous system being particularly vulnerable.

Acute vs. Chronic Oxygen Toxicity

Oxygen toxicity can manifest differently depending on the concentration of oxygen and the duration of exposure. This is often categorized into acute and chronic effects.

Acute (Central Nervous System) Toxicity: This type of toxicity can occur with exposure to very high partial pressures of oxygen, such as those encountered in hyperbaric oxygen therapy or during deep-sea diving. Symptoms can appear relatively quickly and include visual disturbances, tinnitus (ringing in the ears), nausea, and muscle twitching. In severe cases, it can lead to generalized convulsions or seizures.
Chronic (Pulmonary) Toxicity: This form results from breathing moderately high concentrations of oxygen for extended periods, such as in patients on mechanical ventilation. The effects primarily target the lungs, causing symptoms like coughing, chest pain, and shortness of breath due to damage to the air sacs and airways. In some instances, it can lead to more serious conditions like pulmonary edema and atelectasis (lung collapse).

Effects of Increased Oxygen Levels on Key Body Systems

The Lungs

The lungs are often the first organs to show signs of oxygen toxicity because they are in direct contact with the gas. Damage to the delicate lung tissues can impair gas exchange and lead to serious respiratory problems. This is particularly concerning for premature infants, who are at a higher risk of developing bronchopulmonary dysplasia, a chronic lung disease, from prolonged high oxygen exposure.

The Central Nervous System (CNS)

Under high pressure, excessive oxygen can cross the blood-brain barrier and affect the CNS. The symptoms can be quite varied and unpredictable, but early signs like irritability, anxiety, and dizziness can progress to more severe neurological issues, including seizures. While these acute effects are often reversible upon reduction of the oxygen level, the risk is a significant concern in certain medical procedures and professions.

The Eyes

Ocular complications are another known risk of high oxygen levels. In infants, prolonged exposure can lead to retinopathy of prematurity (ROP), which affects blood vessels in the retina and can cause visual impairment or blindness. In adults, hyperbaric oxygen therapy can sometimes cause temporary visual changes like myopia or, in rare long-term cases, accelerate cataract formation.

Other Bodily Effects

While the lungs, CNS, and eyes are most susceptible, excessive oxygen can affect other tissues as well. Oxidative damage can impact red blood cells, the heart, and the endocrine glands. In patients with pre-existing lung conditions like chronic obstructive pulmonary disease (COPD), high oxygen levels can suppress their natural breathing drive, leading to carbon dioxide narcosis.

Comparison of Oxygen Levels and Effects


Oxygen Level (Partial Pressure)	Potential Scenario	Primary Effects and Symptoms
Normal (approx. 21% at sea level)	Normal atmospheric air	Stable cellular function, no toxicity
Mildly Elevated (e.g., medical use)	Supplemental oxygen therapy	Generally safe for short term, but prolonged use can cause chronic toxicity
Highly Elevated (Hyperbaric)	Hyperbaric Oxygen Therapy (HBOT), Deep-Sea Diving	Acute CNS toxicity, including visual changes, seizures
Moderately Elevated (Prolonged)	Mechanical Ventilation	Chronic pulmonary toxicity, including coughing, lung damage

Prevention and Management of Hyperoxia

The most effective way to manage and prevent oxygen toxicity is to carefully control oxygen levels in clinical settings. Healthcare providers closely monitor patients receiving supplemental oxygen or HBOT to ensure the lowest effective dose is used for the shortest possible duration. This approach is especially critical for vulnerable populations like premature infants. For divers, strict protocols for breathing gas mixtures and dive depths are crucial to avoid acute CNS toxicity. In cases where symptoms appear, reducing the oxygen exposure is the primary treatment. The body's natural repair mechanisms can often reverse the damage once the toxic exposure is removed.

Final Takeaway

While oxygen is non-negotiable for life, the notion that 'more is better' is a dangerous misconception when it comes to oxygen levels in the body. The complex interplay of oxygen, reactive species, and our body's defense mechanisms means that excessive oxygen can be as damaging as a deficiency. It is a potent substance, and its use, especially in a medical context, requires precise control and expert supervision to maximize benefit and minimize harm. For reliable information on respiratory health and oxygen safety, consult resources like the American Thoracic Society.

Disclaimer: This article is for informational purposes only and does not constitute medical advice. Consult a healthcare professional for specific medical concerns or before starting any new treatment.

Frequently Asked Questions

Hyperoxia is the medical term for having excessively high levels of oxygen in the body's tissues and blood. Oxygen toxicity is the harmful effect or damage that occurs as a result of that hyperoxia.

No, it is not possible to get oxygen toxicity from breathing normal atmospheric air at sea level. The concentration of oxygen in the air (about 21%) is well within the safe range for humans. Hyperoxia typically occurs in medical settings involving supplemental oxygen, hyperbaric chambers, or during deep-sea diving.

Individuals most at risk include patients on mechanical ventilators for extended periods, those undergoing hyperbaric oxygen therapy, premature infants, and divers breathing enriched oxygen mixtures at depth. Patients with underlying lung diseases like COPD may also face risks if oxygen is administered improperly.

Symptoms can vary depending on whether the toxicity is acute (affecting the central nervous system) or chronic (affecting the lungs). Common signs include coughing, chest pain, shortness of breath, blurred vision, tinnitus, nausea, and, in severe cases, seizures.

The primary treatment for oxygen toxicity is to reduce or remove the excessive oxygen source. In most cases, symptoms begin to subside once oxygen levels return to a safe range. In severe cases, supportive care is provided to manage specific symptoms.

In many adults, damage from oxygen-induced pulmonary toxicity is often reversible once the high oxygen exposure is stopped. However, in certain cases, particularly with premature infants, long-term complications such as chronic lung disease or eye damage can occur. Long-term neurological damage from acute episodes is rare.

When administered correctly by trained medical professionals for FDA-approved conditions, hyperbaric oxygen therapy (HBOT) is generally safe. The risk of oxygen toxicity is minimized through controlled pressure and exposure times, and providers are prepared to handle potential side effects.