How to cope with sudden climate change and acclimatization more easily

A sudden climate change is easier to cope with if, during the first few days, you don't try to live in the new place with the same stress levels as at home. When moving from a cool to a hot region, it's best to reduce physical activity, avoid the hottest hours, gradually increase the time outdoors, and maintain a normal hydration regime. When traveling to a cold climate, proper clothing, protection from wind and moisture, and gradually increasing the time spent in the cold are crucial. If the altitude also increases sharply, separate altitude acclimatization is required. [1]

The popular expression "I'm acclimatizing" often lumps together several completely different conditions. A headache and poor sleep after an intercontinental flight could be jet lag; weakness and dizziness in the tropics could be a reaction to the heat; a headache after a rapid ascent to the mountains could be a manifestation of altitude sickness; a runny nose and cough could be a respiratory infection, and diarrhea while traveling could be a gastrointestinal infection. These conditions require different approaches. [2]

Adaptation to heat has been particularly well studied. It truly is a physiological process: circulatory and sweating systems gradually improve, and the same physical activity causes a smaller increase in body temperature and heart rate. Most adaptive changes develop within the first week to ten days of regular exposure and moderate activity to hot conditions. [3]

Therefore, the main practical principle after a sudden climate change is simple: do not try to speed up adaptation with medications or heroic exposure to heat or cold - the body, above all, needs time, gradualness, and a reasonable reduction in stress.

What does the body need to “reconfigure” after a climate change?

Moving from one climate region to another simultaneously changes several environmental parameters: temperature, humidity, solar radiation, wind, and sometimes altitude and daylight hours. Each of these factors affects the body in its own way.

When a person arrives from a cool climate to a hot one, the cardiovascular system must direct more blood to the skin, and the sweat glands must actively participate in cooling the body. High humidity hinders sweat evaporation, so the same 30°C can be tolerated very differently in dry and humid climates. The World Health Organization emphasizes that heat risk is determined not by temperature alone, but by its combination with humidity, wind, solar radiation, duration of exposure, and a person's level of acclimatization. [4]

In cold climates, the adaptation mechanism is different. The CDC notes that in cold weather, behavioral adaptations—clothing, wind protection, staying dry, shelter—are significantly more important than the gradual physiological changes so characteristic of heat acclimation. [5]

If altitude changes additionally, the main problem isn't the temperature, but the decrease in oxygen partial pressure. And if the flight crosses several time zones, the internal circadian clock becomes desynchronized. Therefore, there is no universal medical syndrome for "climate change"—there are several different adaptation processes. [6]

Why are the first few days in a hot climate more difficult to bear?

In people accustomed to moderate temperatures, the body's heat-loss system isn't yet optimized for prolonged exposure to heat. When moving, the body must simultaneously supply blood to working muscles and increase skin blood flow to remove excess heat.

After repeated exposure to heat, the body gradually adapts: sweating begins earlier and becomes more efficient, electrolyte loss through sweat decreases, circulation stabilizes, and, with the same exertion, heart rate and core temperature increase less. The CDC classifies these changes as the key signs of heat acclimatization. [7]

Some adaptation may occur even with regular exposure to warm temperatures, but full acclimatization requires repeated physical activity in the heat. The CDC Yellow Book notes that most changes develop within approximately ten days of regular exposure, with reductions in the duration and intensity of activity being particularly important during the first few days. [8]

Therefore, the scenario of “flying in from a cool country and walking 25 kilometers around the city at 35°C on the first day” creates a completely different physiological load than the same walk after several weeks of living in such a climate.

How long does acclimatization last after moving to a hot climate?

There is no exact number of days that is the same for everyone. Many of the major physiological changes associated with heat adaptation develop significantly within 7-10 days, but the rate varies with age, physical fitness, intensity of exposure, temperature, and health status. NIOSH uses a period of approximately 7-14 days for gradual adaptation to hot work. [9]

For tourists, the process often remains incomplete. Vacations can last only a week, and the first few days are spent during the period of greatest unaccustomedness to heat. Therefore, the CDC advises travelers who haven't had time to acclimatize in advance to limit the duration and intensity of physical activity during the first week of their trip. [10]

This doesn't mean you have to spend the first seven days in a hotel. The goal is to ease the transition: a short walk in the morning is better than a multi-hour hike in the afternoon, and a leisurely swim or walk is wiser than an intense workout on the very first day.

How to behave during the first 2-3 days after arriving in a hot country

It is better to view the first day as an adaptation period, rather than as a need to immediately complete the entire tourist program.

If possible, long walks and exercise should be postponed until the morning or evening. The WHO recommends avoiding strenuous activity during the hottest hours, seeking shade, and regularly spending time in a cool place during periods of intense heat. [11]

It makes sense to gradually increase physical activity. If you've been walking 5,000 steps a day at home, a trip to the tropics isn't the best time to suddenly switch to hours-long hikes in the sun.

Clothing should be light and loose, but still protect the skin from the sun. For extended outdoor activities, the CDC also recommends a hat and UV protection. [12]

Do I need to drink more on purpose?

In hot climates, fluid requirements can actually increase because the body loses more water through sweat. This is especially noticeable during long walks, sports, or working outdoors.

But the "drink as much as possible" rule is also incorrect. The CDC notes two opposing problems: dehydration increases heat stress, while forced consumption of large volumes of water beyond physiological needs increases the risk of hyponatremia—an excessive decrease in sodium in the blood. [13]

For typical hiking activities, it's usually sufficient to have constant access to water and drink regularly throughout the day, especially when thirsty. During long hours of physical activity and intense sweating, replenishing salt through food may also be necessary. [14]

There is no reason to start taking diuretics, salt tablets, or large doses of electrolytes on your own just because you have arrived in a hot country.

Should I take electrolytes when changing climates?

For normal rest, walking, and moderate activity, most healthy people do not require an electrolyte drink on a regular basis.

The CDC Yellow Book notes that during light to moderate exercise in hot weather, electrolyte drinks offer no clear advantage over plain water. For prolonged activity with heavy sweating, salt can be obtained from regular food or appropriate beverages. [15]

A completely different situation occurs with vomiting or severe diarrhea. Here, a person loses both water and electrolytes, so oral rehydration solutions may be used if fluid loss is significant. Traveler's diarrhea is more often caused by intestinal pathogens and should not be automatically attributed to "acclimatization." [16]

Why might a headache and weakness occur in the heat?

Headache, fatigue, dizziness and nausea can indeed accompany poor heat tolerance.

The CDC notes that heat exhaustion in non-acclimatized people sometimes develops gradually over several days and may be mistaken for a vague "summer illness": weakness, fatigue, headache, dizziness, decreased appetite, nausea, vomiting, and even diarrhea are possible. [17]

Therefore, pronounced symptoms should not be automatically considered a necessary part of normal acclimatization. A person who feels unwell in the heat should stop exerting themselves, move to a cooler place, and rehydrate.

If severe confusion, loss of coordination, seizures, or loss of consciousness occurs, it may be heatstroke, a condition that requires emergency medical attention.[18]

Can the body swell during acclimatization?

Minor swelling of the hands and feet has indeed been reported during the first few days of exposure to hot climates. The CDC Yellow Book classifies so-called heat edema as a mild condition that occurs with initial exposure to heat; it usually resolves on its own. [19]

It is not recommended to use diuretics for this type of edema: they can increase fluid loss and interfere with normal thermal adaptation. [20]

But persistent, pronounced swelling, especially one-sided, painful, or accompanied by shortness of breath, can no longer be reliably explained by climate.

What changes when you move to a very humid climate

High humidity primarily impairs the body's ability to cool itself through the evaporation of sweat.

A person can sweat profusely, but the skin remains wet because water evaporates slowly. Therefore, high temperatures combined with high humidity create a significantly greater heat load than the same temperature in dry air. [21]

This is why physical activity in tropical climates can feel much more difficult at first, even if the temperature does not seem extreme.

In such a climate, cool rooms, shade, light clothing, reduced intensity of exercise, and gradual adaptation are especially beneficial.

What happens when we move to a dry climate?

Dry air affects primarily not “general acclimatization”, but the surface of the eyes, skin and respiratory tract.

Low humidity contributes to dry mucous membranes. For example, the CDC notes that dry airplane air, with humidity levels of approximately 10-20%, can cause dry eyes and upper respiratory tract. Similar discomfort is possible when traveling to very dry climates. [22]

A modern review of humidity research also links very dry air to increased eye and airway irritation and impaired mucociliary clearance, the mechanism by which mucus removes particles from the airways.[23]

Therefore, dry nose or eyes in a new location does not necessarily mean an infection or “poor immunity.”

How to transition from hot to cold weather more easily

When moving to a cold climate, the key is not trying to "harden yourself in three days," but rather properly managing heat loss.

The CDC recommends wearing multiple layers of clothing: a base layer helps wick away moisture, a middle layer traps warmth, and an outer layer protects from wind and precipitation. The most important principle is to stay dry, as wet clothing significantly accelerates cooling. [24]

The combination of cold, wind, and moisture is especially dangerous. A person can tolerate dry frost relatively well, but quickly become chilled in warmer temperatures under strong winds or in wet clothing.

Shivering is a normal way to increase heat production, but severe shivering signals that the body is experiencing significant cold stress. Confusion and loss of coordination are dangerous signs of progressive hypothermia. [25]

Do I need to “harden myself” before the trip?

For a regular tourist trip, a special hardening program is not mandatory.

In the case of heat, gradual heat acclimatization has been much better studied: repeated moderate exercise in hot conditions over several days does indeed cause measurable physiological changes. [26]

For cold weather, the CDC places more emphasis on behavioral protection—clothing, wind insulation, staying dry, and proper gear—than on trying to achieve significant physiological adaptations upfront.[27]

Therefore, there is no medical point in deliberately freezing before a winter vacation.

Climate change and jet lag are not the same thing.

This is one of the most important differences.

Jet lag is caused not by climate, but by rapidly crossing time zones. The internal circadian clock continues to operate on its current schedule for some time, while local time has already changed. This results in sleep disturbances, daytime sleepiness, decreased attention, general malaise, and sometimes gastrointestinal symptoms. [28]

According to the CDC Yellow Book, adaptation typically occurs more quickly when traveling west: an average of about 1.5 hours of internal clock shift per day versus about one hour per day when traveling east. These are average values, not exact timeframes for each individual. [29]

Light is one of the key cues for resetting the circadian rhythm. Properly timed exposure to light in the morning or evening can accelerate synchronization, but the optimal timing depends on the flight destination and the number of time zones crossed. [30]

Therefore, a person can simultaneously experience both jet lag and adaptation to a hot climate—for example, after a flight from Europe to Southeast Asia.

Why does acclimatization mean something completely different in the mountains?

If the journey involves a significant elevation above sea level, the main factor is the reduction in partial pressure of oxygen.

At an altitude of approximately 3,050 meters, the percentage of oxygen in the air does not change, but the atmospheric pressure drops, resulting in the partial pressure of inhaled oxygen being only about 69% of that at sea level. In a newly arrived person, blood oxygen saturation therefore becomes lower. [31]

Acute high-altitude adaptation is particularly active in the first 3-5 days: pulmonary ventilation increases, oxygenation improves, and cerebral blood flow changes. Longer-term adaptive changes can last weeks or months. [32]

The main way to reduce the risk of altitude sickness is to ascend gradually, rather than trying to compensate for a rapid ascent with good physical fitness.

The CDC and Wilderness Medical Society recommend that after exceeding approximately 10,000 feet (3,000 meters), overnight stays be increased by no more than approximately 1,600 feet (500 meters) per night, and that an additional night of acclimatization be added for approximately every 3,300 feet (1,000 meters) of elevation gain.[33]

How to distinguish altitude sickness from normal fatigue

Acute mountain sickness usually occurs after ascent to altitude and often includes headache combined with one or more of the following symptoms: fatigue, dizziness, nausea, or sleep disturbance.

According to the CDC, typical acute mountain sickness begins and resolves within the first 1-3 days; symptoms that first occur more than three days after arrival without further ascent should no longer be automatically attributed to acute mountain sickness.[34]

If the condition worsens with increasing altitude, further ascent is stopped. In severe cases, descent remains the most important method of reducing hypoxic stress. [35]

Altitude sickness is a good example of why the expression "it's just acclimatization" can sometimes be dangerous.

Can a cold appear due to climate change?

The common cold is caused by viruses, not by the transition from warm to cold or vice versa.

The CDC explicitly defines the common cold as a viral upper respiratory tract infection; it is caused by numerous respiratory viruses. [36]

After a flight, a person can actually become noticeably ill more often: airports, airplanes, public transportation, and tourist attractions create numerous contacts with other people. Dry air can further irritate the mucous membranes and create a feeling of congestion or dryness, which can easily be mistaken for the onset of illness. [37]

Therefore, a runny nose, cough, sore throat or fever should not be automatically attributed to acclimatization.

Is diarrhea a sign of intestinal acclimatization?

Most often, acute traveler's diarrhea is infectious in nature and is not a normal reaction of the body to the climate.

The CDC Yellow Book indicates that traveler's diarrhea is caused by a variety of bacterial, viral, and parasitic pathogens; the risk is primarily related to sanitation, food, and water. [38]

Of course, sudden changes in diet, sleep patterns, and mealtimes can alter bowel frequency, causing constipation or bloating. But sudden, repeated bouts of watery diarrhea, especially with fever, blood in the stool, or vomiting, require consideration of an infectious cause. [39]

This is another example of why the term "acclimatization" should not be used as an explanation for any ill health on holiday.

What to do before traveling if the climate is very different

Most healthy people do not require any special testing before a regular beach or sightseeing vacation.

It's helpful to research in advance the typical temperatures and humidity at your destination, the altitude, the likelihood of extreme heat or cold, and the nature of your planned physical activity.

If you're planning a vacation at altitude, it's important to plan your ascent speed. If you plan to walk a lot or exercise in the heat, it's best to keep the first few days of your hike less intense.

People with chronic heart, lung, or kidney disease, diabetes, or other conditions that affect thermoregulation and exercise tolerance should discuss their trip with their doctor beforehand, especially if heat, high altitude, or extreme cold is expected. The CDC notes that chronic medical conditions and certain medications can significantly alter tolerance to extreme temperatures. [40]

Do I need to change my medications due to the hot climate?

On my own - no.

Some medications can actually affect thermoregulation, blood pressure, sweating, or water-salt balance, so the risk may increase in extreme heat. The CDC Yellow Book lists chronic medical conditions and a number of medications as factors that increase the risk of heat illness. [41]

However, this doesn't mean you should stop taking medications before traveling. The decision depends on the specific condition and medication.

If a person is taking multiple regular medications and is traveling to an area with extreme heat or high altitude, it is best to discuss the issue with their doctor before traveling.

Does alcohol help you relax during acclimatization?

From the point of view of the body's adaptation, this is a bad strategy.

During the first few days at high altitude, the CDC recommends avoiding alcohol for about the first 48 hours, as it can impair sleep, affect breathing, and make it difficult to assess symptoms of altitude sickness.[42]

Alcohol is also undesirable in hot weather: it can affect vascular response, water balance, and the ability to objectively assess the onset of overheating.

If a person simultaneously slept poorly after a flight, ate little, spent the day in the sun, and drinks alcohol, determining the cause of weakness, dizziness, or nausea becomes even more difficult.

Do vitamins, adaptogens, and immunomodulators help?

For normal climate adaptation, international recommendations emphasize not supplements but gradual exposure, adjustments to physical activity, clothing, hydration, cooling or cold protection, and proper ascent to altitude. [43]

There is no special universal vitamin regimen that can make the body adapt more quickly to heat, cold, humidity, and time zones simultaneously in just a few days.

This is especially important because the guise of an "acclimatization remedy" can overlook the real cause of symptoms - such as heat exhaustion, infection, or altitude sickness.

A practical plan for the first days after a sudden climate change

Situation	What is reasonable to do in the first days?
From cool to hot	Reduce stress, be more active in the morning and evening, and avoid prolonged activity in extreme heat.
From dry to humid climate	Take into account the deterioration of sweat evaporation, reduce the intensity of physical activity
From a humid climate to a dry one	Monitor dry eyes and mucous membranes, maintain normal fluid intake
From warm to cold	Wear layers of clothing, protect yourself from the wind, and keep your clothes dry.
To the heights	Rise gradually and avoid heavy loads during the first few days.
Across several time zones	Switch to a local sleep and eating schedule, use light to reset the routine
After an overnight flight	Don't plan to do maximum physical activity on the first day
In case of severe fever	Use shade, cooling and cool rooms

This scheme reflects different adaptation mechanisms, rather than an attempt to treat all conditions with a single diagnosis of “acclimatization.” [44]

Who copes worse with sudden climate change?

Older adults and young children are more sensitive to extreme heat. Elderly people have reduced mechanisms for heat loss and are more likely to have chronic illnesses and medications that affect thermoregulation. [45]

Extra caution is required for people with cardiovascular or renal diseases and diabetes, as well as those with sweating disorders and certain skin diseases. [46]

A separate group is made up of people with lung and heart disease when traveling to high altitudes, because the decrease in partial pressure of oxygen can significantly increase the load on an already limited respiratory or cardiovascular system. [47]

Physical fitness helps one cope with stress more easily, but it does not make a person completely protected from heat stroke or altitude sickness.

When feeling unwell is no longer considered acclimatization

Normal adaptation to a new climate should not be used as a universal explanation for severe or progressive disease.

When a person is feverish, warning signs include confusion, severe loss of coordination, seizures, loss of consciousness, or a state in which the person becomes severely unresponsive. This may be consistent with heatstroke and requires emergency care. [48]

In the cold, the dangers include the cessation of effective shivering while cooling continues, marked lethargy, clumsiness, and confusion. [49]

At altitude, do not continue ascending if symptoms of acute mountain sickness worsen. Impaired coordination, severe shortness of breath at rest, or changes in consciousness require immediate assessment and usually descent. [50]

High fever with respiratory symptoms, severe diarrhea, blood in the stool, or persistent vomiting should not be automatically attributed to climate change. Colds are caused by viruses, and traveler's diarrhea is often infectious in nature. [51]

What is often misunderstood

"Acclimatization is an illness that must be overcome." No. It's the process of the body adapting to new conditions. Many people experience virtually no noticeable discomfort.

"If you feel bad for the first three days, it's definitely the climate." No. Jet lag, infections, foodborne illnesses, altitude sickness, dehydration, and heat exhaustion can all appear around the same time after arrival. [52]

"You can get used to the heat in a day." Full physiological changes develop gradually; most require several days of regular exposure, often around 7-10 days. [53]

"The more you spend in the sun, the faster you get used to it." Heat acclimatization requires gradual adaptation, not extreme overheating. Excessive heat stress increases the risk of heat illness. [54]

"A cold is a normal part of climate change." A cold is a viral infection. Cold or air conditioning can affect the subjective comfort of the mucous membranes, but they do not in themselves create a virus. [55]

"Any diarrhea on vacation is a gut restructuring." Acute traveler's diarrhea is often related to infectious agents and food or water safety.[56]

Key points from experts

Howard D. Backer, MD, MPH, is a physician with the University of California Student Health Service in Berkeley, specializing in emergency and preventive medicine. His current University Health Services profile certifies his medical education, training in emergency and preventive medicine, and a Master of Public Health degree. Backer is a co-author of the chapter "Heat and Cold Illness in Travelers" in the CDC Yellow Book 2026. [57]

In this chapter, the authors emphasize the fundamental difference between heat and cold: heat tolerance is significantly improved by physiological acclimatization, whereas behavioral protective measures play a central role in cold. For non-acclimatized travelers to hot climates, it is recommended to reduce the intensity and duration of activity during the first week. [58]

Peter H. Hackett, MD, is a physician and altitude medicine specialist and Assistant Clinical Professor in the Department of Medicine, Pulmonary Sciences & Critical Care at the University of Colorado. His university profile recognizes his position and long-standing research on altitude physiology and altitude-related diseases. [59]

Hackett is one of the authors of the current CDC Yellow Book chapter on high-altitude travel. It emphasizes gradual ascent as a key principle for preventing altitude sickness: it is the rate of elevation gain and the time for adaptation, not physical fitness per se, that determines the safety of traveling to high altitudes. [60]

Frequently Asked Questions

How many days does acclimatization last after a climate change?

There is no single time frame. When adapting to heat, most physiological changes develop within approximately 7-10 days of regular exposure, but the rate varies among individuals. [61]

Is it normal to feel weak during the first few days in a hot country?

Mild fatigue is possible, especially with unusual exertion. However, severe weakness, dizziness, nausea, or an inability to continue normal activity may be signs of heat exhaustion and require rest and cooling. [62]

Do you need to sleep more during the first few days?

Extra rest can be beneficial after a long flight, especially if you also experience jet lag. However, the need for sleep is more related to sleep deprivation and circadian disruption than to air temperature per se. [63]

Is it possible to walk a lot immediately after arrival?

Yes, if the climate is moderate and you feel well. When moving into extreme heat, the CDC recommends limiting the intensity and duration of physical activity for the first week. [64]

Should you avoid air conditioning?

There's no need to completely abandon air conditioning. Cool rooms help reduce heat stress during hot weather. The WHO recommends spending part of the day in a cool place during high temperatures. [65]

Can air conditioning cause colds?

The air conditioner itself does not cause viral colds. Colds are caused by respiratory viruses. [66]

Should I take vitamin C before traveling?

There is no specific, proven vitamin regimen for preventing climate acclimatization. International recommendations emphasize gradual adaptation, temperature control, clothing, hydration, and exercise adjustment.

Why is it so hard to walk in the tropics during the first few days?

The body has not yet fully adapted to increased skin blood flow and sweating, and high humidity can impair sweat evaporation. Thermal tolerance usually improves over time. [67]

Is it possible to speed up acclimatization through exercise?

Moderate, repeated physical activity in hot weather does contribute to heat acclimatization, but the intensity should be increased gradually. Extreme exercise in the first few days increases the risk of overheating rather than beneficially accelerating the process. [68]

What should you do if you develop a runny nose and fever while on vacation?

Do not automatically assume this is a climate change. Colds and other respiratory illnesses have infectious causes; if symptoms are severe, the possibility of infection should be assessed. [69]

Can climate change cause intestinal upset?

Changes in diet and routine can affect bowel function, but sudden, severe diarrhea while traveling is often infectious in nature. [70]

Is acclimatization in the mountains the same as at sea?

No. In the mountains, the main problem can be hypoxia due to a decrease in oxygen pressure, so a gradual increase in altitude is required. This is a separate physiological process. [71]

When should I see a doctor after moving?

If symptoms are severe, progressive, last longer than expected, or include loss of consciousness, confusion, severe shortness of breath, high fever, severe diarrhea, blood in the stool, or neurological impairment, they cannot be safely attributed to acclimatization alone.

Conclusion

A sudden change in climate is more easily tolerated if you give the body a few days to adapt and reduce the difference between the usual and new loads. When transitioning to a hot climate, a gradual increase in activity, avoiding strenuous exercise during the hottest hours, maintaining proper hydration, and regularly cooling down are especially beneficial. The key physiological changes associated with heat acclimatization develop gradually, rather than over a few hours. [72]

When transitioning to cold weather, clothing, wind protection, and staying dry are crucial. Traveling to high altitude requires a separate strategy for gradual ascent, and after flying across several time zones, poor sleep and drowsiness are more often explained by jet lag than temperature. [73]

And most importantly: "acclimatization" shouldn't be used as an explanation for every ailment you experience while traveling. Infections, heat exhaustion, altitude sickness, and other conditions can begin in the first few days of travel and sometimes require completely different treatment.