question: Why our body isn't comfortable in cold water like it is in hot water?
comment: Water has higher thermal conductivity than air, meaning it can transfer or remove heat faster. 60F might feel fine in air because while your body is \~98.6F, the air can't remove heat fast enough to offset natural heat generation, but for water it can. Thus your skin detects the loss of heat from itself and triggers a "cold" response.
passages: Taking advantage of the cooling properties of water may help attenuate the consequences of heat sensitivity. In a study done by White et al. (2000), exercise pre-cooling via lower body immersion in water of 16–17 °C for 30 minutes allowed heat sensitive individuals with MS to exercise in greater comfort and with fewer side effects by minimizing body temperature increases during exercise. Hydrotherapy exercise in moderately cool water of 27–29 °C water can also be advantageous to individuals with MS. Temperatures lower than 27 °C are not recommended because of the increased risk of invoking spasticity.
  
  Section::::History.
   Blood flow to the muscles is lower in cold water, but exercise keeps the muscle warm and flow elevated even when the skin is chilled. Blood flow to fat normally increases during exercise, but this is inhibited by immersion in cold water. Adaptation to cold reduces the extreme vasoconstriction which usually occurs with cold water immersion.
   Heat transfers very well into water, and body heat is therefore lost extremely quickly in water compared to air, even in merely 'cool' swimming waters around 70F (~20C). A water temperature of can lead to death in as little as one hour, and water temperatures hovering at freezing can lead to death in as little as 15 minutes. This is because cold water can have other lethal effects on the body, so hypothermia is not usually a reason for drowning or the clinical cause of death for those who drown in cold water.
   Sitting in water above normal body temperatures can cause drowsiness which may lead to unconsciousness and subsequently result in drowning. The U.S. Consumer Product Safety Commission (CPSC) recommends that water temperatures never exceed 40 degrees Celsius. A temperature of 37 degrees is considered safe for a healthy adult. Soaking in water above 39 degrees Celsius can cause fetal damage during the first three months of pregnancy.
   Thermoregulation in humans
  
  As in other mammals, thermoregulation in humans is an important aspect of homeostasis. In thermoregulation, body heat is generated mostly in the deep organs, especially the liver, brain, and heart, and in contraction of skeletal muscles. Humans have been able to adapt to a great diversity of climates, including hot humid and hot arid. High temperatures pose serious stress for the human body, placing it in great danger of injury or even death. For humans, adaptation to varying climatic conditions includes both physiological mechanisms resulting from evolution and behavioural mechanisms resulting from conscious cultural adaptations.
   In these ways, winter swimmers can survive both the initial shock and prolonged exposure. Nevertheless, the human organism is not suited to freezing water: the struggle to maintain blood temperature (by swimming or conditioned metabolic response) produces great fatigue after thirty minutes or less.
  
  Section::::Cold shock response in bacteria.
   Dogs are even more susceptible than humans to heat stroke in cars, as they cannot produce whole-body sweat to cool themselves. Leaving the dog at home with plenty of water on hot days is recommended instead, or, if a dog must be brought along, it can be tied up in the shade outside the destination and provided with a full water bowl.
  
  Section::::Prevention.
   Humans adapted to heat early on. In Africa, the climate selected for traits that helped us stay cool. Also, we had physiological mechanisms that reduced the rate of metabolism and that modified the sensitivity of sweat glands to provide an adequate amount for cooldown without the individual becoming dehydrated . 
   As in other mammals, thermoregulation is an important aspect of human homeostasis. Most body heat is generated in the deep organs, especially the liver, brain, and heart, and in contraction of skeletal muscles. Humans have been able to adapt to a great diversity of climates, including hot humid and hot arid. High temperatures pose serious stresses for the human body, placing it in great danger of injury or even death. For example, one of the most common reactions to hot temperatures is heat exhaustion, which is an illness that could happen if one is exposed to high temperatures, resulting in some symptoms such as dizziness, fainting, or a rapid heartbeat. For humans, adaptation to varying climatic conditions includes both physiological mechanisms resulting from evolution and behavioural mechanisms resulting from conscious cultural adaptations. The physiological control of the body’s core temperature takes place primarily through the hypothalamus, which assumes the role as the body’s “thermostat.” This organ possesses control mechanisms as well as key temperature sensors, which are connected to nerve cells called thermoreceptors. Thermoreceptors come in two subcategories; ones that respond to cold temperatures and ones that respond to warm temperatures. Scattered throughout the body in both peripheral and central nervous systems, these nerve cells are sensitive to changes in temperature and are able to provide useful information to the hypothalamus through the process of negative feedback, thus maintaining a constant core temperature.
   By the late 1930s more than 2,000 hot- or cold-springs health resorts were operating in the United States. This number had diminished greatly by the 1950s and continued to decline in the following two decades. In the recent past, spas in the U.S. emphasized dietary, exercise, or recreational programs more than traditional bathing activities.
  
  Up until recently, the public bathing industry in the U.S. remained stagnant. Nevertheless, in Europe, therapeutic baths have always been very popular, and remain so today. The same is true in Japan, where the traditional hot springs baths, known as "onsen", always attracted plenty of visitors.
   Two conflicting safety issues affect water heater temperature—the risk of scalding from excessively hot water greater than , and the risk of incubating bacteria colonies, particularly "Legionella", in water that is not hot enough to kill them. Both risks are potentially life-threatening and are balanced by setting the water heater's thermostat to . The European Guidelines for Control and Prevention of Travel Associated Legionnaires’ Disease recommend that hot water should be stored at and distributed so that a temperature of at least and preferably is achieved within one minute at points of use.
   Section::::Physiological adaptations.:Acclimatization.
  
  When humans are exposed to certain climates for extended periods of time, physiological changes occur to help the individual adapt to hot or cold climates. This helps the body conserve energy.
  
  Section::::Physiological adaptations.:Acclimatization.:Cold.
   The opah utilizes retia mirabilia to conserve heat, making it the newest addition to the list of regionally endothermic fish. Blood traveling through capillaries in the gills must carry cold blood due to their exposure to cold water, but retia mirabilia in the opah's gills are able to transfer heat from warm blood in arterioles coming from the heart that heats this colder blood in arterioles leaving the gills. The huge pectoral muscles of the opah, which generate most of the body heat, are thus able to control the temperature of the rest of the body.
  
  Section::::Mammals.
   Thomas Guidott set up a medical practice in the English town of Bath in 1668. He became interested in the curative properties of the waters. In 1676, he wrote "A discourse of Bathe, and the hot waters there. Also, Some Enquiries into the Nature of the water". This brought the health-giving properties of the hot mineral waters to the attention of the aristocracy. Doctors and quacks set up spa towns such as Harrogate, Bath, Matlock and Buxton soon after taking advantage of mineral water from chalybeate springs.
  
  Section::::History.:18th century.
  
  Section::::History.:18th century.:England.
   It is recommended for the temperature of tap water not to exceed 38 — 45 °C to avoid discomfort and scalding. The technical implementation is complicated by the necessity to keep warm water at a temperature of 55 – 60 °C to inhibit the growth of legionella bacteria. 
  
  Water at 60 °C can induce scalding injuries in less than 3 seconds, while it takes 10 seconds to get an injury at 57 °C and 1.5 to 2 minutes to achieve an injury in 52 °C hot water. 
   Heat shock proteins (HSPs) are expressed during exposure to high temperatures and is a characteristic held by most organisms. In some species of nototheniids, this trait is not expressed. The trait is not expressed because of the extreme cold of the Southern Oceans leading to upregulation of Hsp70. HSP expression indicates that regulation of Hsp70 occurred once during speciation, showing that it is a trait of most, if not all Antarctic notothenioids possess.
   Scalding is a serious concern with any water heater. Human skin burns quickly at high temperature, in less than 5 seconds at , but much slower at — it takes a full minute for a second degree burn. Older people and children often receive serious scalds due to disabilities or slow reaction times. In the United States and elsewhere it is common practice to put a tempering valve on the outlet of the water heater. The result of mixing hot and cold water via a tempering valve is referred to as "tempered water".
   Sitting in a bathtub of tepid or cool water (immersion method) can remove a significant amount of heat in a relatively short period of time. It was once thought that immersion in very cold water is counterproductive, as it causes vasoconstriction in the skin and thereby prevents heat from escaping the body core. However, a British analysis of various studies stated: "this has never been proven experimentally. Indeed, a recent study using normal volunteers has shown that cooling rates were fastest when the coldest water was used." The analysis concluded that iced water immersion is the most-effective cooling technique for exertional heat stroke. No superior cooling method has been found for "non-exertional heat stroke". Thus, aggressive "ice-water" immersion remains the gold standard for "life-threatening heat stroke".
   Temperature can be an essential element of the taste experience. Food and drink that—in a given culture—is traditionally served hot is often considered distasteful if cold, and vice versa. For example, alcoholic beverages, with a few exceptions, are usually thought best when served at room temperature or chilled to varying degrees, but soups—again, with exceptions—are usually only eaten hot. A cultural example are soft drinks. In North America it is almost always preferred cold, regardless of season.
  
  Section::::Further sensations and transmission.:Starchiness.
   Winter swimming isn't dangerous for healthy persons, but should be avoided by individuals with heart or respiratory diseases, obesity, high blood pressure and arrhythmia, as well as children and the elderly. Through conditioning, experienced winter swimmers have a greater resistance to effects of the cold shock response.
   BULLET::::- Homeothermy: Although most fish are exclusively ectothermic, there are exceptions. Certain species of fish maintain elevated body temperatures. Endothermic teleosts (bony fish) are all in the suborder Scombroidei and include the billfishes, tunas, including a "primitive" mackerel species, "Gasterochisma melampus". All sharks in the family Lamnidae – shortfin mako, long fin mako, white, porbeagle, and salmon shark – are endothermic, and evidence suggests the trait exists in family Alopiidae (thresher sharks). The degree of endothermy varies from the billfish, which warm only their eyes and brain, to bluefin tuna and porbeagle sharks who maintain body temperatures elevated in excess of 20 °C above ambient water temperatures. "See also gigantothermy". Endothermy, though metabolically costly, is thought to provide advantages such as increased muscle strength, higher rates of central nervous system processing, and higher rates of digestion.
   In Patrick O'Brian's novel "Post Captain" (1972), Diana Villiers' mentally troubled cousin, Edward Lowndes, upon learning that Doctor Maturin is a naval surgeon, remarks, "Very good—you are "upon" the sea but not "in" it: you are not an advocate for cold baths. The sea, the sea! Where should we be without it? Frizzled to a mere toast, sir; parched, desiccated by the simoom, the dread simoom."
   To cope with low temperatures, some fish have developed the ability to remain functional even when the water temperature is below freezing; some use natural antifreeze or antifreeze proteins to resist ice crystal formation in their tissues. Amphibians and reptiles cope with heat loss by evaporative cooling and behavioral adaptations. An example of behavioral adaptation is that of a lizard lying in the sun on a hot rock in order to heat through radiation and conduction.
  
  Section::::Classification of animals by thermal characteristics.:Endothermy.
   (Illustrated by a still lake, where the surface water can be comfortably warm for swimming but deeper layers be so cold as to represent a danger to swimmers, the same effect as gives rise to notices in London's city docks warning 'Danger Cold Deep Water).
   Cold and heat adaptations in humans
  
  Cold and heat adaptations in humans are a part of the broad adaptability of "Homo sapiens". Adaptations in humans can be physiological, genetic, or cultural, which allow people to live in a wide variety of climates. There has been a great deal of research done on developmental adjustment, acclimatization, and cultural practices, but less research on genetic adaptations to cold and heat temperatures.
  