Last updated: October 2026
Flying is safe for most people, but the aircraft cabin has lower pressure and drier air than the ground, and long flights mean hours without moving. If you are pregnant, have a medical condition, recently had surgery or travel with medication, a little planning avoids problems at the airport and on board.
What happens to your body on a flight
- Lower oxygen: the cabin is pressurized to the equivalent of 1,800 to 2,400 meters (6,000 to 8,000 feet). Healthy people do not notice it, but people with heart or lung disease may need extra oxygen.
- Gas expansion: trapped air expands, which causes ear pain on descent and can be dangerous after some surgeries or diving.
- Dry air: humidity is very low, which dries eyes, skin and airways.
- Sitting still for hours: increases the risk of blood clots in the legs (deep vein thrombosis, DVT) in people with risk factors.
Pregnant passengers
- With a normal pregnancy, flying is generally considered safe. Many doctors see the second trimester (about weeks 14 to 27) as the most comfortable time to travel.
- From week 28, most airlines ask for a letter or certificate from your doctor or midwife confirming your due date and that you are fit to fly.
- Last week to fly: most airlines do not accept passengers after week 36 (some after week 35 or 37) for a single pregnancy, or after week 32 for twins or more.
- Check your airline's rules for the return flight too: the limit is counted on the date of each flight.
- Choose an aisle seat, walk regularly, drink water and ask your doctor about compression stockings.
- Make sure your travel insurance covers pregnancy and childbirth abroad: many policies do not.
Babies
- Most airlines accept babies from 7 to 14 days old, depending on the airline.
- Feeding or giving a pacifier during takeoff and landing helps with ear pressure.
- Babies need their own passport or ID on international trips.
Medical conditions and recent surgery
Ask your doctor before flying if you have:
- Recent surgery, especially abdominal, chest, eye or brain surgery.
- A recent heart attack, stroke or unstable heart condition.
- Serious lung disease, or need oxygen on the ground.
- A recent blood clot, or a history of DVT.
- A recent fracture with a plaster cast (the leg can swell inside it).
- A contagious disease.
If you need medical oxygen, a stretcher or other special arrangements, the airline will usually ask for a medical form (often called MEDIF) completed by your doctor, days in advance.
Diving before flying
To reduce the risk of decompression sickness, the Divers Alert Network recommends waiting:
- At least 12 hours after a single no-decompression dive.
- At least 18 hours after several dives or several days of diving.
- Substantially longer than 18 hours after dives that required decompression stops.
Carrying medication
- Keep medicines in your cabin bag, in their original packaging, with enough for the whole trip plus a few extra days in case of delays.
- Carry the prescription or a doctor's letter with the generic names of the medicines, ideally in English.
- Medically necessary liquids (insulin, syrups, liquid nutrition) are allowed in larger amounts than 100 ml. Tell the security staff and show them separately.
- Syringes and needles are allowed with the medicine that needs them.
- Controlled medicines: some common medicines, such as strong painkillers, sleeping pills or ADHD medication, are restricted in countries like Japan, the United Arab Emirates or Singapore, and may need a permit. Check with the embassy before traveling.
- If you take medication at set times, plan how to adjust it to the time zone change with your doctor.
On long flights
- Drink water regularly; limit alcohol and caffeine.
- Get up and walk every one or two hours when it is safe, and move your feet and ankles while seated.
- Wear comfortable, loose clothes. If you have risk factors for DVT, ask your doctor about compression stockings.
- To reduce jet lag, adapt to the local schedule as soon as you arrive and get daylight.
- If you have a cold or blocked nose, ear pain on descent can be stronger: a decongestant spray before landing may help (ask your pharmacist).
Vaccines and health requirements
- Some countries require a yellow fever vaccination certificate, especially if you come from or connected through a risk area. The certificate becomes valid 10 days after vaccination and is valid for life.
- Visit a travel medicine clinic 4 to 8 weeks before traveling to tropical destinations.
- Check that routine vaccines, such as measles, are up to date.
- Buy travel insurance with good medical cover: it is the most important protection abroad.
Also useful: Passengers with special needs.
Official sources
- CDC – Travelers' Health
- World Health Organization – Travel and health
- Divers Alert Network – Guidelines for flying after diving
- TSA – Medical conditions and disabilities at security
This guide is general information and does not replace medical advice. Consult your doctor before traveling if you have any health condition.