Acclimatization

Acclimatization is the physiological adjustment of an organism to a change in its environment that allows continued performance and homeostasis. It occurs in many species, including humans, and can involve responses to temperature, altitude, humidity, photoperiod, and radiation. Acclimatization is usually a gradual, reversible process that develops over days to weeks and may be incomplete if the stress is severe or prolonged.

In common usage, acclimatization describes adaptive changes in natural environments, while acclimation refers to similar adaptations simulated under laboratory or controlled conditions. The terms are sometimes used interchangeably in the literature, which can cause inconsistencies in definitions.

Examples: High altitude acclimatization involves increased ventilation, a rise in red blood cell mass, and changes in acid-base balance, typically occurring over several days to weeks. Heat acclimatization includes earlier and more efficient sweating, higher skin blood flow, and expanded plasma volume, improving tolerance to exercise in hot conditions. Cold acclimatization can involve reduced shivering threshold and improved non-shivering thermogenesis, especially in colder climates. These changes optimize oxygen transport, heat regulation, and metabolic efficiency.

Limits and considerations: Acclimatization capacity varies with genetics, age, fitness, and prior exposure. Rapid exposure to extreme stress can lead to acute maladaptations such as altitude sickness or heat illness. Practical approaches to promote acclimatization include gradual exposure, hydration, appropriate rest, and monitoring during travel, exercise, or occupational activity.