Individual risk factors for altitude illness

Altitude illness can occur in any individual, and there is no certain way to predict its onset. The main predictor is a history of an altitude illness. Few patient-specific factors affect risk, and most stable medical conditions do not affect risk. Limited evidence suggests that obesity and current respiratory infection increase the riskInstitute for Altitude Medicine, 2016-2018 (Accessed August 2021)Luks, 2007 Luks, 2017. The effect of age is difficult to assess; children, adolescents and adults older than 40 years may be less at risk than adults younger than 40 years, but this may reflect behavioural differences (eg rate of ascent).

Cardiac and respiratory conditions that cause pulmonary hypertension may specifically increase the risk of high-altitude pulmonary oedema (HAPE)Institute for Altitude Medicine, 2016-2018 (Accessed August 2021)Luks, 2007.

Contraindications to high-altitude travel are few, but some conditions may be exacerbated or destabilised.

  • Coagulopathy can be affected by an increase in blood viscosity at high altitude.
  • People with sickle cell disease are at risk of sickling crises in hypoxic conditions and are generally advised not to travel to high altitude.
  • Risk of miscarriage and other adverse pregnancy outcomes is increased at altitude, therefore such travel is not recommended without specialist review.

Other risks to consider before travel to high altitude are conditions that commonly develop in high-altitude areas, including:

  • cough—this is almost universal with increasing duration of stay at high altitudes. It can be severe and cause fractured ribs and poor sleep. Cough is very difficult to alleviate other than with descent, but on its own it is not an indicator of high-altitude pulmonary oedema (HAPE) (see Altitude illness syndromes for HAPE criteria).
  • disturbed sleep—suppression of respiratory drive at night in high altitudes causes irregular (periodic) breathing with apnoeic pauses of up to 30 seconds, producing symptoms similar to those of obstructive sleep apnoea
  • cold-related illnesses such as hypothermia and frostbite
  • photokeratitis (snow blindness)
  • corneal thickening can cause blurring or visual loss in people who have had refractive surgery
  • retinal haemorrhages—these are common and asymptomatic unless near the macula; if visual loss occurs, urgent descent is required.