International travelers may be subject to certain stresses that may lower resistance to disease, such as crowding, disruption of usual eating and drinking habits, and time changes with “jet lag” contributing to a disturbed pattern of the sleep and wakefulness cycle. These conditions of stress can lead to nausea, indigestion, fatigue, or insomnia. Complete adaptation depends on the number of time zones crossed but may take a week or more.

Heat and cold can be directly or indirectly responsible for some diseases and can give rise to serious skin conditions. Dermatophytoses such as athlete's foot are often made worse by warm, humid conditions.

Excessive heat and humidity alone, or immoderate activity under those conditions, may lead to heat exhaustion due to salt and water deficiency and to the more serious heat stroke or hyperthermia. The ultraviolet rays of the sun can cause severe and very debilitating sunburn in lighter-skinned persons.

Excessive cold affects persons who may be inadequately dressed and particularly the elderly; it can lead to hypothermia and to frost-bite of exposed parts of the body.

Breathing and swallowing dust when traveling on unpaved roads or in arid areas may be followed by nausea and malaise, and may cause increased susceptibility to infections of the upper respiratory tract.

Traveling in high altitudes may lead to insomnia, headache, nausea, and altitude sickness, even in young and healthy persons, and can cause distress to those with cardiac or pulmonary conditions. Individual susceptibility to acute mountain sickness is highly variable. Travelers who are at greatest risk are those who ascend rapidly to tourist sites in the Andes and the Himalayas. Acetazolamide has been shown, under both simulated and actual climbing conditions, to hasten the process of acclimatization to high altitudes. The recommended dosage to prevent acute mountain sickness is 250 mg every 8–12 hours, with medication initiated 24–48 hours before, and continued during ascent. Acetazolamide should not be taken by individuals who are allergic to sulfonamides.