the effectiveness of evaporative cooling depends upon humidity. wet-bulb temperature, which takes humidity into account, or more complex calculated quantities such as wet-bulb globe temperature (wbgt), which also takes solar radiation into account, give useful indications of the degree of heat stress and are used by several agencies as the basis for heat-stress prevention guidelines. (wet-bulb temperature is essentially the lowest skin temperature attainable by evaporative cooling at a given ambient temperature and humidity.) a sustained wet-bulb temperature exceeding 35 °c (95 °f) is likely to be fatal even to fit and healthy people unclothed in the shade next to a fan; at this temperature, environmental heat gain instead of loss occurs. as of 2012, wet-bulb temperatures only very rarely exceeded 30 °c (86 °f) anywhere, although significant global warming may change this. in cases of heat stress caused by physical exertion, hot environments, or protective equipment, prevention or mitigation by frequent rest breaks, careful hydration, and monitoring body temperature should be attempted. however, in situations demanding one is exposed to a hot environment for a prolonged period or must wear protective equipment, a personal cooling system is required as a matter of health and safety. there are a variety of active or passive personal cooling systems; these can be categorized by their power sources and whether they are person- or vehicle-mounted. because of the broad variety of operating conditions, these devices must meet specific requirements concerning their rate and duration of cooling, their power source, and their adherence to health and safety regulations. among other criteria are the user's need for physical mobility and autonomy. for example, active-liquid systems operate by chilling water and circulating it through a garment; the skin surface area is thereby cooled through conduction. this type of system has proven successful in certain military, law enforcement, and industrial applications. bomb-disposal technicians wearing special suits to protect against improvised explosive devices (ieds) use a small, ice-based chiller unit that is strapped to one leg; a liquid-circulating garment, usually a vest, is worn over the torso to maintain a safe core body temperature. by contrast, soldiers traveling in combat vehicles can face microclimate temperatures in excess of 65 °c (149 °f) and require a multiple-user, vehicle-powered cooling system with rapid connection capabilities. requirements for hazmat teams, the medical community, and workers in heavy industry vary further. treatment the underlying cause must be removed. mild hyperthemia caused by exertion on a hot day may be adequately treated through self-care measures, such as increased water consumption and resting in a cool place. hyperthermia that results from drug exposure requires prompt cessation of that drug, and occasionally the use of other drugs as counter measures. antipyretics (e.g., acetaminophen, aspirin, other nonsteroidal anti-inflammatory drugs) have no role in the treatment of heatstroke because antipyretics interrupt the change in the hypothalamic set point caused by pyrogens; they are not expected to work on a healthy hypothalamus that has been overloaded, as in the case of heatstroke. in this situation, antipyretics actually may be harmful in patients who develop hepatic, hematologic, and renal complications because they may aggravate bleeding tendencies. when body temperature is significantly elevated, mechanical cooling methods are used to remove heat and to restore the body's ability to regulate its own temperatures. passive cooling techniques, such as resting in a cool, shady area and removing clothing can be applied immediately. active cooling methods, such as sponging the head, neck, and trunk with cool water, remove heat from the body and thereby speed the body's return to normal temperatures. drinking water and turning a fan or dehumidifying air conditioning unit on the affected person may improve the effectiveness of the body's evaporative cooling mechanisms (sweating). 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. when the body temperature reaches about 40 °c (104 °f), or if the affected person is unconscious or showing signs of confusion, hyperthermia is considered a medical emergency that requires treatment in a proper medical facility. in a hospital, more aggressive cooling measures are available, including intravenous hydration, gastric lavage with iced saline, and even hemodialysis to cool the blood. epidemiology hyperthermia affects those who are unable to regulate their body heat, mainly due to environmental conditions. the main risk factor for hyperthermia is the lack of ability to sweat. people who are dehydrated or who are older may not produce the sweat they need to regulate their body temperature. high heat conditions can put certain groups at risk for hyperthermia including: physically active individuals, soldiers, construction workers, landscapers and factory workers. some people that do not have access to cooler living conditions, like people with lower socioeconomic status, may have a difficult time fighting the heat. people are at risk for hyperthermia during high heat and dry conditions, most commonly seen in the summer. various cases of different types of hyperthermia have been reported. a research study was published in march 2019 that looked into multiple case reports of drug induced hyperthermia. the study concluded that psychotropic drugs such as anti-psychotics, antidepressants, and anxiolytics were associated with an increased heat-related mortality as opposed to the other drugs researched (anticholinergics, diuretics, cardiovascular agents, etc.). a different study was published in june 2019 that examined the association between hyperthermia in older adults and the temperatures in the united states. hospitalization records of elderly patients in the us between 1991 and 2006 were analyzed and concluded that cases of hyperthermia were observed to be highest in regions with arid climates. the study discussed finding a disproportionately high number of cases of hyperthermia in early seasonal heat waves indicating that people were not yet practicing proper techniques to stay cool and prevent overheating in the early presence of warm, dry weather. in urban areas people are at an increased susceptibility to hyperthermia. this is due to a phenomenon called the urban heat island effect. since the 20th century in the united states, the north-central region (ohio, indiana, illinois, missouri, iowa, and nebraska) was the region with the highest morbidity resulting from hyperthermia. northeastern states had the next highest. regions least affected by heat wave-related hyperthermia causing death were southern and pacific coastal states. northern cities in the united states are at greater risk of hyperthermia during heat waves due to the fact that people tend to have a lower minimum mortality temperature at higher latitudes. in contrast, cities residing in lower latitudes within the continental us typically have higher thresholds for ambient temperatures. in india, hundreds die every year from summer heat waves, including more than 2,500 in the year 2015. later that same summer, the 2015 pakistani heat wave killed about 2,000 people. an extreme 2003 european heat wave caused tens of thousands of deaths. causes of hyperthermia include dehydration, use of certain medications, using cocaine and amphetamines or excessive alcohol use. bodily temperatures greater than 37.5–38.3 °c (99.5-101.0 °f) can be diagnosed as a hyperthermic case. as body temperatures increase or excessive body temperatures persist, individuals are at a heightened risk of developing progressive conditions. greater risk complications of hyperthermia include heat stroke, organ malfunction, organ failure, and death. there are two forms of heat stroke; classical heatstroke and exertional heatstroke. classical heatstroke occurs from extreme environmental conditions, such as heat waves. those who are most commonly affected by classical heatstroke are very young, elderly or chronically ill. exertional heatstroke appears in individuals after vigorous physical activity. exertional heatstroke is displayed most commonly in healthy 15-50 year old people. sweating is often present in exertional heatstroke. the associated mortality rate of heatstroke is 40 to 64%. research hyperthermia can also be deliberately induced using drugs or medical devices, and is being studied and applied in clinical routine as a treatment of some kinds of cancer. research has shown that medically controlled hyperthermia can shrink tumours. this occurs when a high body temperature damages cancerous cells by destroying proteins and structures within each cell. hyperthermia has also been researched to investigate whether it causes cancerous tumours to be more prone to radiation as a form of treatment; which as a result has allowed hyperthermia to be used to compliment other forms of cancer therapy. various techniques of hyperthermia in the treatment of cancer include local or regional hyperthermia, as well as whole body techniques.