Getting acquainted with heat is usually a 10 to 15-day affair. During this time, the body readjusts itself physiologically. The sweating rate increases, thereby increasing the evaporative heat loss. There is a progressive reduction in rectal temperature and pulse rate. Other changes like cardiac output, blood volume, blood flow to the periphery, increased excretion of salt in the sweat, etc come back to normal after the preliminary increase during the first few days of exposure to heat. Once the body settles dwon to the new condition, it is better equipped to fight the heat. Once can get acclimatise to heat even while staying in a cold climate by exposing oneself to artificially created heat for two hours a day; acclimatisation will be complete in three to four weeks.

The conservation of salt in sweatm after acclimatisation, is a result of an increased secretion of the hormone called aldosterone. The increase in sweat secretion reduces urine output to a mere 300ml to 500ml per day. (In winter it is about 1500ml per day.) The degree of acclimatisation depends upon the temperature a person is exposed to and his level of activity. A sedentary person is less acclimatise than a person who does physical work in a hot environment. There is also an upper limit beyond which further adaptation is not possible. Normal residents of tropical countries are better adapted than acclimatised sojourners. This is manifested in more economical sweating-probably a water conservation method-without jeopardising heat dissipation.

Acclimatisation lasts for two weeks after heat exposure but rapidly disappears after a month. However, some phychological effects are retained. People withh previous experience sho better tolerance even after years compared to people who have never been exposed to heat before.

For an Indian, the comfortable temperature ranges between 74 degree and 85 degree F (23.3 to 29.4 degree C). At higher temperatures, there is a steady fall in working efficiency, more in mental efficiency.