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Why Can’t Humans Breathe Underwater

Why Can’t Humans Breathe Underwater? Human Limits

Why can’t humans breathe underwater? It’s a question that has puzzled scientists and curious minds alike, yet the simple answer lies in the fundamental differences between air and water and how our lungs function.

As land-dwelling creatures, we are equipped with the remarkable ability to inhale and exhale air to sustain our lives. 

However, our respiratory system faces a significant challenge regarding underwater environments. But why is it so? To understand this phenomenon, we need to answer the question, 

Why can’t humans breathe underwater?

Humans cannot breathe underwater due to two main reasons. Firstly, our lungs don’t have enough surface area to absorb oxygen from the water. While our lungs are designed to extract oxygen from the air, they are not equipped to extract oxygen from water. 

The second reason is that our lungs are adapted to handle air rather than water. Our respiratory system is specifically designed to take in air, with a much higher oxygen concentration than water.  

How Long Can An Average Human Being Stay Under Water?

The average time to hold their breath underwater ranges from 30 to 90 seconds. However, this time can vary depending on factors such as breath training, medical condition, and smoking habits. 

While most individuals can only hold their breath briefly, exceptional cases defy this expectation.

Have you ever heard of the Bajau people, also known as sea nomads, from Southeast Africa? 

These remarkable individuals can hold their breath for up to 13 minutes! While this may seem like a scene straight out of a science fiction scene, it is true. 

Research has shown that the Bajau people underwent a genetic adaptation caused by natural selection resulting in larger spleens than other humans. 

So, what explains the Bajau people’s extraordinary ability to hold their breath for such extended periods? It lies in their large spleens. 

The spleen stores oxygenated blood, allowing them to stay underwater for longer. This genetic adaptation has been developed over generations through natural selection, enabling the Bajau people to thrive in their underwater environment.

What Happens If You Breathe Underwater?

In this scenario, the air is replaced with water. The lungs, which normally act as the exchange medium for oxygen and carbon dioxide, cannot extract oxygen from water or remove carbon dioxide from the body. 

As a result, carbon dioxide builds up in the body. The body’s natural reflex is to breathe involuntarily, but instead of taking in oxygen, this reflex only adds more water into the lungs. 

After approximately two minutes of breathing underwater, you will begin to weaken and ultimately pass out. 

This is because your body is not receiving the necessary oxygen to function properly. After about five minutes without oxygen, brain damage can begin to occur. 

This is a critical stage, as the brain requires a constant oxygen supply to function properly. After approximately six minutes without oxygen, certain brain death may occur.

If you are fortunate enough to be rescued while still conscious, lying in a slanted position is essential. 

This will allow any water that has entered the lungs to drain, reducing the risk of further complications. Depending on the severity of the situation, CPR may be needed to help restore breathing and circulation.

Close monitoring is necessary even after recovery and once breathing normally because secondary drowning can occur. 

If water irritates the lung lining, it can lead to pulmonary edema, where fluid accumulates in the lungs.

What Happens When You Hold Your Breathe?

When you hold your breath, your body is deprived of the necessary oxygen for performing vital functions. 

Even though you’re not inhaling fresh oxygen, your body still uses the available oxygen and releases carbon dioxide as a waste product.

As you continue to hold your breath, carbon dioxide levels within your body start to rise since there is no way for it to escape. Eventually, this triggers an involuntary reflex that compels you to start breathing again.

You may feel a burning sensation in your lungs. If you continue to hold your breath, your diaphragm muscles will contract in an attempt to force breathing, which can cause pain.

You will lose consciousness if you do not resume your normal breathing pattern. On land, your body will automatically initiate breathing to replenish the oxygen it needs. However, if you are underwater, this is when the risk of drowning becomes a concern. 

How Does Human Respiratory System Work?

The human respiratory system is a complex network of organs and tissues that work together to ensure the proper exchange of oxygen and carbon dioxide in our bodies. It is a system that allows us to breathe and sustain life. 

The process begins with the inhalation of air through the nose or mouth. The air then travels down the trachea, or windpipe, a tube connecting the throat to the lungs. 

The trachea branches out into smaller tubes called bronchi, which further divide into even smaller passages called bronchioles. These bronchioles eventually lead to tiny air sacs called alveoli.

Within the alveoli, the exchange of gases takes place. Oxygen from the inhaled air diffuses across the thin walls of the alveoli into the surrounding capillaries, while carbon dioxide, a waste product of metabolism, moves in the opposite direction. 

The oxygen-rich blood then travels back to the heart to be pumped throughout the body, providing oxygen to cells and tissues.

Meanwhile, the carbon dioxide-rich blood returns to the lungs and is exhaled during exhalation. 

Exhalation is the release of carbon dioxide from our bodies through the nose or mouth. It is a passive process that occurs as our diaphragm relaxes, pushing air out of our lungs.

How Do Under Water Animals Breathe?

Underwater animals have fascinating adaptations that allow them to breathe in their aquatic environment. Let’s explore some of the ways underwater animals obtain oxygen for survival.

1. Absorbing oxygen through their skin

Some species can absorb oxygen directly from their skin. For example, amphibians like frogs and salamanders have thin, permeable skin that allows oxygen to pass through and into their bloodstream. 

The process is called cutaneous respiration. Some aquatic insects like water beetles and dragonfly nymphs also use this respiration method to extract oxygen from the water.

2. Using gills

Fishes are prime example of gill-breathing creatures. Gills are specialized organs composed of thin filaments containing numerous blood vessels. 

As water passes over the gills, oxygen diffuses from the water into the blood vessels, and carbon dioxide is released. 

This exchange of gases occurs due to a high concentration gradient between the oxygen-rich water and the deoxygenated blood in the gill filaments.

3. Gulping air into the gas bladder

Like some fish and aquatic insects, certain species have a gas bladder or swim bladder, which serves multiple functions, including buoyancy control and respiration.

These animals gulp air at the water’s surface and transfer it into the gas bladder. Oxygen is extracted from the air inside the gas bladder, and carbon dioxide is released. These animals can control their buoyancy in the water by regulating the gas in the bladder.

A Thought For Brainers 

If you have a curious mind, you must have already asked yourselves, if humans can’t breathe underwater, what about the human fetus? How do they survive in the amniotic fluid up until the last time of birth? 

It has been shown that in the last stages of pregnancy, the fetus ‘practice breathing’ by inhaling and exhaling the amniotic fluid. The process is crucial for their lung development and preparing them for life outside the womb. 

However, it is important to note that the fetus doesn’t rely on its lungs for oxygen supply in the womb as we do with air. Instead, oxygen is obtained from the mother’s bloodstream through the placenta. 

The oxygen-rich blood is then delivered to the fetus’s brain and other body parts, ensuring an adequate oxygen supply without a buildup of carbon dioxide. 

This mechanism allows the fetus to survive and develop in the amniotic fluid environment. However, breathing underwater as an adult human presents a different challenge. 

In this scenario, when we inhale water instead of air, the oxygen supply is depleted, and carbon dioxide accumulates rapidly. The lack of oxygen becomes a critical issue, leading to the inability to sustain life.

Therefore, while the fetus does indeed “breathe” by practicing inhaling and exhaling amniotic fluid, this is not its primary source of oxygen.


Why can’t humans breathe underwater? While humans have made technological advancements and developed various diving apparatuses to explore underwater environments, we can still not naturally respire underwater. 

The inability of humans to breathe underwater can be attributed to several factors. Our respiratory system is specifically designed for breathing air, not water. 

Additionally, humans do not possess gills like fish, which allow them to extract oxygen from water. 

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