Even though the plane is pressurized, it isn’t pressurized to sea level. Most cabins mimic the air pressure of an altitude between 5,000 and 8,000 feet.
- Hypoxia (Lower Oxygen): At cruising altitude, there is roughly 15% less oxygen available in the cabin air. Healthy bodies compensate by slightly increasing heart and breathing rates.
- Gas Expansion (Boyle’s Law): As the plane climbs and pressure drops, the air trapped in your body (ears, sinuses, gut) expands by about 25%.
- Low Humidity: Cabin humidity is often below 20% (normal indoor air is 30–50%). This dries out your mucous membranes, which are your first line of defense against germs.
1. The “Non-Sick” Passenger: Low-level risks
Even if you’re in peak health, a long-haul flight carries specific risks:
| Risk | Cause | Prevention |
| DVT (Blood Clots) | Immobility and cramped seating. | Walk every hour; perform compression socks while seated. |
| Barotrauma | Pressure changes during takeoff/landing. | Chewing gum or use the “Valsalva maneuver” (gently blowing with nose pinched). |
| Dehydration | Extreme dry cabin air. | Drink water; avoid excessive alcohol/caffeine which are diuretics. |
| Infection | Proximity to others (not the recycled air, which is HEPA-filtered). | Wash hands frequently; avoid touching your face. |
2. The “Mildly Sick” Passenger: common pitfalls
If you have a common cold or minor infection, the plane environment can turn “annoying” into “painful.”
- The “Ear Pop” Danger: If your Eustachian tubes are swollen from a cold, your ears cannot equalize pressure. This can lead to severe pain, fluid buildup, or even a ruptured eardrum.
- Tip: Use a decongestant spray 30 minutes before descent (example: Oxymetazoline).
- Sinus Pressure: Trapped air in infected sinuses expands during the climb, causing intense “vacuum headaches.”
- Contagion: You are in a high-touch environment. If you have a fever or a persistent cough, it’s often more ethical (and safer for your recovery) to postpone.
3. The “Clinically Ill” Passenger: High-Risk Conditions
For those with chronic or serious conditions, the lowered oxygen and pressure can be dangerous.
Respiratory & Heart Conditions
If your body already struggles to oxygenate your blood (COPD, Heart Failure, Severe Anemia), the 15% drop in oxygen can lead to hypoxemia.
If you cannot walk 50 meters or climb one flight of stairs without getting severely winded, you may need supplemental oxygen to fly safely.
Recent Surgery
Because gas expands in the body, flying within 10–14 days of abdominal or chest surgery is often prohibited. Expanding gas can put pressure on internal sutures, potentially causing them to tear.
The “No-Fly” List (Contraindications)
Doctors generally advise against flying if you have:
The “No-Fly” List (Contraindications)
- An untreated Pneumothorax (collapsed lung).
- Recent eye surgery involving a gas bubble.
- Unstable Angina or a very recent Heart Attack (typically within the 3 weeks after the event).
- Highly contagious diseases (Measles, Tuberculosis, etc.).
- Infants < 48h old (avoid a flight for the 7 days avec the delivery if possible)
- > 36 weeks of pregnancy
- Decompression sickness after diving (avoid airplane travel 24h after this activity)
- Infections of ENT
- Recent stroke
Final Takeaway
For the healthy, flying is a test of hydration and patience. For the sick, it is a physiological stress test. If you are ever unsure, the “Fit to Fly” certificate from your GP is your best friend not just for your health, but because airlines have the right to deny boarding to anyone who appears visibly unstable.
Reference: Aerospace Medical Association
