Environmental hazards and health.

Significant health hazards to the traveller arise from altitude, heat, cold and water. Altitude-induced illness encompasses the benign but common syndrome of acute mountain sickness and also life-threatening pulmonary and cerebral oedema; inadequate acclimatization and rapid ascent are important precipitating factors in each case. Prophylaxis and up to date choices of treatment are discussed in the context of underlying physiological changes. Heat illnesses include exhaustion and heat stroke; they result from increased core temperature and/or physiological responses including peripheral vasodilation and sweating. Preventive measures include acclimatization, ample water without added salt, and matching dress and exercise to the environment. Cold environments pose risk of hypothermia and local cold injury which include frostbite and non-freezing cold injury; as frostnip is only diagnosed after treatment, it is a category of limited usefulness. Prevention of each disorder requires correct clothing and equipment and good training. Other hazards include immersion, and flying too soon after diving.