Low Oxygen: Signs and Symptoms of Hypoxia

Medically Reviewed By Angelica Balingit, MD
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Hypoxia is a condition in which the body’s tissues do not have enough oxygen. The most common symptom of ongoing hypoxia is shortness of breath. This article will explain hypoxia (low oxygen), including the signs and symptoms of low oxygen, its causes, and how doctors approach treatment. It will also discuss the outlook for people with hypoxia.

Hypoxia vs. hypoxemia

female laying on couch with oxygen mask
Danil Nevsky/Stocksy United

Hypoxia means low oxygen. People often use the term “hypoxia” to mean low blood oxygen. However, the medical name for low oxygen level in the blood is hypoxemia. Hypoxemia is a cause of hypoxia, but there are other causes of hypoxia in a person with normal blood oxygen levels.

Hypoxia can develop suddenly or with time and with differing levels of severity. “Acute hypoxia” is another term describing sudden hypoxia. It may be the result of an emergency medical condition, such as a pulmonary embolism (PE), pulmonary edema, sepsis, or a heart attack. 

Hypoxia that develops over time is usually due to chronic underlying problems, such as heart failure or chronic obstructive pulmonary disease (COPD).

How oxygen gets into tissues

Normally, we breathe at a regular rate. When we take in air, it goes into alveoli, tiny sacs in the lungs.

The alveoli transfer oxygen into blood flowing through very small capillary blood vessels. Once the blood reaches capillaries in the tissues, it releases oxygen that goes into the cells of the tissues.

The cells have structures called mitochondria. These use the oxygen to make energy for the cell.

Hypoxia can result when any of these processes goes wrong. 

Effect of hypoxia on the body

Hypoxia causes a variety of symptoms that can range in severity. The heart may start to beat faster, trying to get more blood to the tissues. Breathing rate may also increase to get more oxygen into the blood. Headache, confusion, or chest pain may occur.

Depending on the cause, other symptoms, such as fever, may be present. Hypoxia can damage organs and become fatal without treatment.

People who have an underlying breathing or circulatory condition are more likely to develop hypoxia. Traveling to a high altitude can also cause hypoxia. 

Getting treatment for signs and symptoms of low oxygen levels

Treating hypoxia involves giving oxygen and treating the underlying condition.

Seek prompt medical care for shortness of breath at rest or with slight exertion, or if it worsens with physical activity.

Seek immediate medical care (call 911) for serious symptoms, such as:

  • trouble breathing
  • confusion
  • rapid heartbeat
  • pale skin or nails
  • reduced consciousness

Low oxygen may indicate that an underlying lung or circulatory problem is getting worse. Contact your doctor right away if you have a chronic condition and notice new or changing symptoms.

What are the symptoms of hypoxia?

Hypoxia signs and symptoms vary in severity and with the underlying cause. The most common symptom of hypoxia is shortness of breath with exertion. Sometimes, shortness of breath may occur even at rest.

Other symptoms may be present, including: 

Seek immediate medical care (call 911) for:

  • breathing that sounds harsh or grating
  • chest pain or fast heartbeat
  • cyanosis, which is a pale or bluish discoloration of the skin, mucous membranes, and nails
  • distended neck veins
  • headache, confusion, restlessness, or altered consciousness or ability to think clearly
  • severe shortness of breath or trouble breathing

What causes hypoxia?

Hypoxia (low oxygen in tissues) can develop when there is a problem with the way the body gets oxygen, transports it, or uses it. Possible causes of hypoxia are listed in the sections that follow.

Impaired access: Hypoxemia (low blood oxygen)

Low levels of oxygen in the blood will reduce the amount of oxygen the body’s organs and tissues receive. Causes of hypoxemia include:

  • high altitude, where there is less oxygen in the air
  • anemia
  • COPD
  • PE
  • pneumonia

Impaired transport: Heart and circulatory problems

Heart failure and other circulatory problems can cause a person to become hypoxic. In some cases of these conditions, the heart is not able to pump enough blood to the tissues. The person may or may not have hypoxemia. With impaired oxygen delivery, specific tissues, such as the brain, or the whole body, can become hypoxic.

Impaired use: Inflammation and poisoning

Inflammation and poisons (carbon monoxide, cyanide, hydrogen sulfide) can cause problems with how the body’s cells extract and use oxygen. In this scenario, cells cannot get or use oxygen from the blood. The lungs and heart are normal, but the body is still hypoxic.

What are the risk factors for hypoxia?

A number of factors increase the risk of developing hypoxia. Most of them are medical conditions that can cause problems with the body’s ability to get, transport, or use oxygen. Risk factors for hypoxia include:

  • medications that slow breathing
  • anemia, severe bleeding, or being at a high altitude
  • heart problems, including heart failure or heart attack
  • inflammatory conditions, including allergic reactions and edema
  • lung conditions such as:
    • asthma
    • COPD
    • pleural effusion
    • pneumonia
    • PE
    • pulmonary edema
    • airway obstruction
  • neuromuscular diseases such as:
  • restricted chest movement due to:
  • poisonings by substances such as:
    • carbon monoxide
    • cyanide
    • smoke inhalation

How do you prevent hypoxia?

It is not always possible to prevent hypoxia. Prevention mainly relies on avoiding or controlling underlying medical conditions. Seeking treatment right away for disease flares, such as with asthma and COPD, can help prevent hypoxia from becoming serious.

How do doctors diagnose hypoxia?

Your doctor will take a medical history, perform an exam, and order testing. During the exam, your doctor will listen to your heart and lungs and evaluate your breathing. The exam may also involve a neurological exam and checking your ski, arms, and legs.

Tests your doctor can use to diagnose hypoxia and its underlying cause include:

Questions your doctor may ask you include:

  • What symptoms are you experiencing?
  • Are your symptoms constant or do they come and go?
  • How severe are your symptoms?
  • What, if anything, seems to make your symptoms better or worse?
  • What medical conditions do you have?
  • What medications do you take?

Learn more about low oxygen levels here.

How do you treat hypoxia? 

Treating hypoxia has three components:

Maintaining open airways

To keep the airways of the lungs open, treatments may include:

  • bronchodilator medicines to relax the airways
  • clearing the airways via chest physical therapy
  • incentive spirometry
  • positive pressure ventilation, such as continuous positive airway pressure (CPAP) or bilevel positive airway pressure

Get the facts about COPD, sleep apnea, and CPAP machines here.

Increasing oxygen content

To increase the amount of oxygen, treatment involves giving supplemental oxygen. Options include nasal cannula, face masks, positive pressure ventilation, and intubation with a ventilator.

Improving the ability of oxygen to move into the blood

This involves treating the underlying condition. Treatment will depend on the condition and may involve medications or other treatments. For example, a doctor may prescribe steroids to reduce inflammation.

Ultimately, doctors can use extracorporeal membrane oxygenation if all other options are not working. This is a form of life support. It exchanges gases in and out of the blood like the lungs would normally do.

If you receive supplemental oxygen, get tips for oxygen therapy here.

What are the potential complications of hypoxia?

Hypoxia deprives your organs and tissues of the oxygen they need to live. Both acute and chronic hypoxia can lead to organ damage, which may be permanent. Left untreated, acute hypoxia can be fatal.

The outlook for people with hypoxia depends on the underlying cause and its treatment, the affected area of the body, and how long the tissues have been without oxygen. For example, brain cells begin to die after only 5 minutes without oxygen.

A person without underlying health conditions can withstand and adapt to hypoxic environments, such as people living at very high altitudes. However, the outcome for people with hypoxia is not as favorable when the condition is due to heart or lung conditions that are difficult to treat or resistant to treatment.


Hypoxia is a state of low oxygen in the body’s tissues. It can be body wide or local, such as low oxygen in the hands or feet. Hypoxia is not the same as hypoxemia, which is low oxygen levels in the blood.

Causes of low oxygen include high altitude, anemia, COPD, heart failure, inflammatory conditions, and carbon monoxide poisoning, among other causes.

Treating hypoxia may include a combination of medication, respiratory therapy, oxygen therapy, and life support in extreme situations.

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Medical Reviewer: Angelica Balingit, MD
Last Review Date: 2022 Mar 9
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THIS TOOL DOES NOT PROVIDE MEDICAL ADVICE. It is intended for informational purposes only. It is not a substitute for professional medical advice, diagnosis or treatment. Never ignore professional medical advice in seeking treatment because of something you have read on the site. If you think you may have a medical emergency, immediately call your doctor or dial 911.
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