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The Physiological Hazards of High-Altitude Flight: What Happens to the Human Body

Updated: Dec 19, 2025

High-altitude flight exposes pilots and passengers to an environment the human body was never designed to tolerate without help. As altitude increases, air pressure decreases, and trapped gases expand. These changes can lead to a range of physiological hazards—some uncomfortable, some painful, and some potentially dangerous.


Understanding how altitude affects the sinuses, teeth, gastrointestinal tract, and lungs helps pilots anticipate problems and make safer decisions before and during flight.



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Why Altitude Affects the Body

The key factor in most altitude-related physiological issues is Boyle’s Law, which states that as pressure decreases, the volume of a gas increases. In flight, this means any air trapped in body cavities will expand as altitude increases—and must be able to escape or equalize.


When it can’t, problems arise.


Sinus Congestion: Sinus Block and Sinus Squeeze

What Happens

The sinuses are air-filled cavities connected to the nasal passages. Normally, pressure equalizes easily through small openings. However, congestion from:

  • Colds

  • Allergies

  • Sinus infections can block these passages.


As altitude changes:

  • During climb, trapped air expands and may cause pressure or pain

  • During descent, trapped air contracts, creating a vacuum effect called sinus squeeze


Symptoms

  • Facial pain or pressure

  • Headache

  • Pain behind the eyes or forehead

  • In severe cases, nosebleeds


Aviation Risk

Sinus pain can become intense enough to distract or incapacitate a pilot, especially during descent when workload is already high.


Best practice: Avoid flying with nasal or sinus congestion, even if symptoms seem mild on the ground.


Tooth Block: Pain from Trapped Air in Teeth

What Happens

Tooth block occurs when air becomes trapped beneath a dental filling, crown, or in a cavity. As pressure decreases with altitude, this air expands.


Symptoms

  • Sudden, sharp tooth pain

  • Pain during climb or descent

  • Pain that resolves after landing


Aviation Risk

Tooth block pain can be severe and distracting, and it often appears without warning.


Best practice: Maintain good dental health and address dental work issues promptly. Avoid flying at altitude if experiencing unexplained tooth sensitivity.


The Gastrointestinal (GI) Tract: Gas Expansion

What Happens

The stomach and intestines naturally contain gas. As altitude increases, this gas expands.


Symptoms

  • Abdominal bloating

  • Cramping

  • Discomfort or pain

  • Increased belching or flatulence


Aviation Risk

While rarely dangerous, GI discomfort can:

  • Increase distraction

  • Reduce comfort and endurance

  • Add stress during long or high-altitude flights


Best practice: Avoid gas-producing foods before flight and stay hydrated. Symptoms are more noticeable on longer climbs and higher altitudes.


The Lungs: The Most Serious Risk

What Happens

The lungs are particularly vulnerable to pressure changes. If a pilot holds their breath during ascent—even briefly—expanding air in the lungs can cause pulmonary overpressure.


This can lead to:

  • Lung tissue rupture

  • Air leaking into the chest cavity

  • Air entering the bloodstream (arterial gas embolism)


These injuries can occur at surprisingly low altitudes—sometimes with only a few hundred feet of pressure change.


Symptoms

  • Chest pain

  • Shortness of breath

  • Coughing

  • Dizziness or confusion

  • Stroke-like symptoms in severe cases


Aviation Risk

Pulmonary barotrauma and arterial gas embolism are medical emergencies that can be rapidly fatal.


Golden rule: Never hold your breath during ascent. Continuous, relaxed breathing is essential.


Compounding Factors That Increase Risk

Physiological hazards worsen with:

  • Rapid climbs or descents

  • Cold temperatures

  • Dehydration

  • Fatigue

  • Illness

  • Smoking


Night flying and hypoxia can further reduce awareness of developing symptoms.


Pilot Decision-Making and Risk Management

Smart pilots manage physiological risk before takeoff:

  • Don’t fly with colds, sinus congestion, or ear pain

  • Stay current on dental care

  • Eat light, non-gassy meals before high-altitude flights

  • Use supplemental oxygen proactively

  • Make slow, controlled altitude changes when possible


The regulations define legal limits—but physiology defines safe ones.


Final Thought

High-altitude flight challenges the body in subtle but powerful ways. Sinus pain, tooth block, GI discomfort, and lung injuries all stem from the same invisible force: changing pressure. Most of these hazards are preventable with good judgment, conservative planning, and respect for human limitations.


In aviation, altitude doesn’t just affect aircraft performance—it affects pilot performance. Understanding both is essential to flying safely above the ground.



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