People with chronic respiratory diseases, such as asthma, Chronic Obstructive Pulmonary Disease (COPD), and interstitial lung disease, need to be careful when taking a flight.

, explained, "Aeroplane cabins are pressurised, but not to sea level. The cabin pressure in commercial flights usually simulates an altitude of 6,000 to 8,000 feet. At this altitude, oxygen levels are lower than at ground level, which can make breathing more difficult, especially for people with respiratory issues."

She added that for someone with COPD or other lung conditions, this may lead to shortness of breath, reduced oxygen saturation, or even respiratory distress.

Heart diseases are another potential roadblock to safe air travel. These include conditions like Congestive Heart Failure (CHF), recent heart attack, arrhythmias, or uncontrolled high blood pressure.

According to Dr Jain, individuals with heart conditions may experience an increased workload on the heart. Lower oxygen availability can stress the cardiovascular system, possibly leading to chest pain (angina), palpitations, or, in rare cases, cardiac events. "Fluid retention during long flights can also affect people with heart failure, increasing the risk of decompensation," she added.

According to the World Health Organization (WHO), anaemia, characterised by low Red Blood Cells (RBCs) and haemoglobin, is a serious global public health problem, affecting 40% of children 6–59 months of age, 37% of pregnant women, and 30% of women 15–49 years of age worldwide.

Severe anaemia can make air travel potentially dangerous due to the reduced oxygen-carrying capacity of the blood at high altitudes. Lower air pressure in an aeroplane cabin can worsen the effects of anaemia, potentially leading to hypoxia, or oxygen deficiency, and associated symptoms like dizziness, chest pain, and shortness of breath.

Sickle Cell Disease (SCD) is a group of inherited blood disorders characterised by abnormal haemoglobin. According to Dr Jain, it is one of the diseases that can pose difficulty and unexpected challenges during air travel. Again, the culprit is reduced oxygen pressure in the cabin.

A 2022 study published in the International Journal of Travel Medicine and Global Health found that flying may trigger painful crises, damage to the spleen (sometimes requiring surgery), or, in rare cases, sudden death in patients with SCD. To prevent such complications, it’s important to take both general travel precautions and specific medical steps. This includes checking a patient’s fitness to fly and determining whether they’ll need extra oxygen during the flight—something most airlines can provide with a doctor’s prescription, researchers suggested.

For most people with epilepsy, flying doesn’t directly increase the risk of having a seizure. However, some individuals, especially those who have had seizures during flights before or who tend to have frequent seizures, might notice an increase in episodes after air travel. 

Factors like changes in routine, lack of sleep, stress, or missed medication doses can all play a role. That’s why it’s important for people with epilepsy to prepare carefully before flying and speak with their doctor if they have any concerns.

Deep Vein Thrombosis (DVT) can be a serious concern during air travel, particularly on long flights. Sitting for extended periods in cramped spaces can slow blood circulation in the legs, increasing the risk of blood clots. Factors like limited movement, dehydration, and certain pre-existing health conditions can further raise the risk. That’s why it’s important to stay hydrated, move around periodically, and follow preventive measures.

Sharing some of the precautionary measures, Dr Jain said, "People with chronic illnesses should consult their healthcare provider before flying, especially if they’ve had recent symptoms or changes in their medical status. They should ensure their medications are in adequate supply and packed in carry-on luggage. Carrying a brief medical summary, including diagnoses, current medications, allergies, and emergency contact information, is also advisable."

Additionally, for respiratory conditions, a pre-flight oxygen assessment may be necessary. "In some cases, supplemental oxygen during the flight may be recommended, and arrangements must be made with the airline in advance. For heart patients, it’s essential to control blood pressure, maintain hydration, and avoid alcohol or sedatives unless prescribed," Dr Jain added.

Patients at risk of blood clots (like those with a history of DVT) should wear compression stockings and perform leg exercises during the flight.

Several medical conditions often require formal medical clearance before air travel. These include recent surgeries (especially chest or abdominal), recent heart attacks or strokes (within the past few weeks), uncontrolled epilepsy, unstable angina, severe anaemia (haemoglobin < 8 g/dL), and active respiratory infections like tuberculosis.

Pregnant women, particularly those over 28 weeks, may also need a doctor’s note depending on airline policy.

Medical clearance may also be necessary if the passenger needs in-flight oxygen, a stretcher, or other medical support. In such cases, the airline’s medical department may request a “fit-to-fly” certificate or completion of a medical information form (MEDIF) by the attending physician.