Mild disease can be treated with fluids by mouth. In more significant disease spraying with mist and using a fan is useful. For those with severe disease putting them in lukewarm water is recommended if possible with transport to a hospital.

Prevention includes avoiding medications that can increase the risk of heat illness (e.g. antihypertensives, diuretics, and anticholinergics), gradual adjustment to heat, and sufficient fluids and electrolytes.

International Organization for Standardization helps set standards for monitoring environments, analyzing data, and interpreting results.

First aid for heat exhaustion includes:

- Moving the person to a cool place

- Having the patient take off extra layers of clothes

- Cooling the patient down by fanning them and putting wet towels on their body

- Having them lie down and put their feet up if they are feeling dizzy

- Having them drink water or sports drinks – but only if they are awake, not confused nor vomiting

- Turning the person on their side if they are vomiting

Accurate determination of core temperature often requires a special low temperature thermometer, as most clinical thermometers do not measure accurately below . A low temperature thermometer can be placed in the rectum, esophagus or bladder. Esophageal measurements are the most accurate and are recommended once a person is intubated. Other methods of measurement such as in the mouth, under the arm, or using an infrared ear thermometer are often not accurate.

As a hypothermic person's heart rate may be very slow, prolonged feeling for a pulse could be required before detecting. In 2005, the American Heart Association recommended at least 30–45 seconds to verify the absence of a pulse before initiating CPR. Others recommend a 60-second check.

The classical ECG finding of hypothermia is the Osborn J wave. Also, ventricular fibrillation frequently occurs below and asystole below . The Osborn J may look very similar to those of an acute ST elevation myocardial infarction. Thrombolysis as a reaction to the presence of Osborn J waves is not indicated, as it would only worsen the underlying coagulopathy caused by hypothermia.

If a person with heat exhaustion gets medical treatment, Emergency Medical Technicians (EMTs) or doctors and/or nurses may also:

- Give them supplemental oxygen

- Give them intravenous fluids and electrolytes if they are too confused to drink and/or are vomiting

When ambient temperature is excessive, humans and many animals cool themselves below ambient by evaporative cooling of sweat (or other aqueous liquid; saliva in dogs, for example); this helps prevent potentially fatal hyperthermia. 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 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. , wet-bulb temperatures only very rarely exceeded 30 °C 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 is 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 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.

The diagnosis of heat syncope is done during a physical examination. During the physical exam the practitioner will test the blood pressure of the patient, and the pulse. If the patient is experiencing heat syncope the blood pressure will be low, and the pulse will be elevated. Observation of excess sweating will also be a key sign. Finally, the practitioner will ask questions figuring out the history of the patient's symptoms. If the patient developed symptoms while engaging in physical activity and high temperatures it will then be a true case of heat syncope.

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 cool 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, 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.

Appropriate clothing helps to prevent hypothermia. Synthetic and wool fabrics are superior to cotton as they provide better insulation when wet and dry. Some synthetic fabrics, such as polypropylene and polyester, are used in clothing designed to wick perspiration away from the body, such as liner socks and moisture-wicking undergarments. Clothing should be loose fitting, as tight clothing reduces the circulation of warm blood. In planning outdoor activity, prepare appropriately for possible cold weather. Those who drink alcohol before or during outdoor activity should ensure at least one sober person is present responsible for safety.

Covering the head is effective, but no more effective than covering any other part of the body. While common folklore says that people lose most of their heat through their heads, heat loss from the head is no more significant than that from other uncovered parts of the body. However, heat loss from the head is significant in infants, whose head is larger relative to the rest of the body than in adults. Several studies have shown that for uncovered infants, lined hats significantly reduce heat loss and thermal stress. Children have a larger surface area per unit mass, and other things being equal should have one more layer of clothing than adults in similar conditions, and the time they spend in cold environments should be limited. However children are often more active than adults, and may generate more heat. In both adults and children, overexertion causes sweating and thus increases heat loss.

Building a shelter can aid survival where there is danger of death from exposure. Shelters can be of many different types, metal can conduct heat away from the occupants and is sometimes best avoided. The shelter should not be too big so body warmth stays near the occupants. Good ventilation is essential especially if a fire will be lit in the shelter. Fires should be put out before the occupants sleep to prevent carbon monoxide poisoning. People caught in very cold, snowy conditions can build an igloo or snow cave to shelter.

The United States Coast Guard promotes using life vests to protect against hypothermia through the 50/50/50 rule: If someone is in water for 50 minutes, he/she has a 50 percent better chance of survival if wearing a life jacket. A heat escape lessening position can be used to increase survival in cold water.

Babies should sleep at 16-20 °C (61-68 °F) and housebound people should be checked regularly to make sure the temperature of the home is at least 18 °C (64 °F).

Heat alert programs should be developed for implementation when hotter than normal temperatures, or a heat wave occurs.

The basic treatment for heat syncope is like that for other types of fainting: the patient is positioned in a seating or supine position with legs raised. Water containing salt, or another drink containing electrolytes, is administered slowly, and the patient is moved to a cooler area, such as the shade.

The affected person should rest and recover, because heat syncope can lead to heat stroke or heat exhaustion.

To determine the need for referral to a specialized burn unit, the American Burn Association devised a classification system. Under this system, burns can be classified as major, moderate and minor. This is assessed based on a number of factors, including total body surface area affected, the involvement of specific anatomical zones, the age of the person, and associated injuries. Minor burns can typically be managed at home, moderate burns are often managed in hospital, and major burns are managed by a burn center.

The size of a burn is measured as a percentage of total body surface area (TBSA) affected by partial thickness or full thickness burns. First-degree burns that are only red in color and are not blistering are not included in this estimation. Most burns (70%) involve less than 10% of the TBSA.

There are a number of methods to determine the TBSA, including the Wallace rule of nines, Lund and Browder chart, and estimations based on a person's palm size. The rule of nines is easy to remember but only accurate in people over 16 years of age. More accurate estimates can be made using Lund and Browder charts, which take into account the different proportions of body parts in adults and children. The size of a person's handprint (including the palm and fingers) is approximately 1% of their TBSA.

Heat cramps, a type of heat illness, are muscle spasms that result from loss of large amount of salt and water through exercise. Heat cramps are associated with cramping in the abdomen, arms and calves. This can be caused by inadequate consumption of fluids or electrolytes. Frequently, they don't occur until sometime later, especially at night or when relaxing. Heavy sweating causes heat cramps, especially when the water is replaced without also replacing salt or potassium.

Although heat cramps can be quite painful, they usually don't result in permanent damage, though they can be a symptom of heat stroke or heat exhaustion. Heat cramps can indicate a more severe problem in someone with heart disease or if they last for longer than an hour.

In order to prevent them, one may drink electrolyte solutions such as sports drinks during exercise or strenuous work or eat potassium-rich foods like bananas and apples. When heat cramps occur, the affected person should avoid strenuous work and exercise for several hours to allow for recovery.

Polymer fume fever or fluoropolymer fever, also informally called Teflon flu, is an inhalation fever caused by the fumes released when polytetrafluoroethylene (PTFE, known under the trade name Teflon) reaches temperatures of 300 °C (572 °F) to 450 °C (842 °F). When PTFE is heated above 450 °C the pyrolysis products are different and inhalation may cause acute lung injury. Symptoms are flu-like (chills, headaches and fevers) with chest tightness and mild cough. Onset occurs about 4 to 8 hours after exposure to the pyrolysis products of PTFE. A high white blood cell count may be seen and chest x-ray findings are usually minimal.

The polymer fumes are especially harmful to certain birds whose breathing, optimized for rapidity, allows toxins which are excluded by human lungs. Fumes from Teflon in very high heat are fatal to parrots, as well as some other birds (PTFE Toxicosis).

OI is "notoriously difficult to diagnose." As a result, many patients have gone undiagnosed or misdiagnosed and either untreated or treated for other disorders. Current tests for OI (Tilt table test, autonomic assessment, and vascular integrity) can also specify and simplify treatment. (See Dr. Julian Stewart's article, "Orthostatic Intolerance: An Overview" for a more detailed description of OI tests.)

A catastrophic illness is a severe illness requiring prolonged hospitalization or recovery. Examples would include coma, cancer, leukemia, heart attack or stroke. These illnesses usually involve high costs for hospitals, doctors and medicines and may incapacitate the person from working, creating a financial hardship. They are the type intended to be covered by high-deductible health plans. Research indicates that the unusual economic environment of the delivery of catastrophic illness care encourages the use of innovative therapies. Medicare contains a benefit for catastrophic illness.

The treatment options for hypohidrosis and anhidrosis is limited. Those with hypohidrosis should avoid drugs that can aggravate the condition (see medication-causes). They should limit activities that raise the core body temperature and if exercises are to be performed, they should be supervised and be performed in a cool, sheltered and well-ventilated environment. In instances where the cause is known, treatment should be directed at the primary pathology. In autoimmune diseases, such as Sjogren syndrome and systemic sclerosis, treatment of the underlying disease using immunosuppressive drugs may lead to improvement in hypohidrosis. In neurological diseases, the primary pathology is often irreversible. In these instances, prevention of further neurological damage, such as good glycaemic control in diabetes, is the cornerstone of management. In acquired generalized anhidrosis, spontaneous remission may be observed in some cases. Numerous cases have been reported to respond effectively to systemic corticosteroids. Although an optimum dose and regime has not been established, pulse methylprednisolone (up to 1000 mg ⁄ day) has been reported to have good effect.

The primary treatment strategy is to eliminate or discontinue the offensive agent. Supportive therapy, such as ice packs, may be provided to get the body temperature within physiologic range. In severe cases, when the fever is high enough (generally at or above ~104° F or 40° C), aggressive cooling such as an ice bath and pharmacologic therapy such as benzodiazepines may be deemed appropriate.

Heat urticaria presents within five minutes after the skin has been exposed to heat above 43 degrees Celsius (109.4 degrees Fahrenheit), with the exposed area becoming burned, stinging, and turning red, swollen, and indurated.

Sweat is readily visualized by a topical indicator such as iodinated starch (Minor test) or sodium alizarin sulphonate, both of which undergo a dramatic colour change when moistened by sweat. A thermoregulatory sweat test can evaluate the body’s response to a thermal stimulus by inducing sweating through a hot box ⁄ room, thermal blanket or exercise. Failure of the topical indicator to undergo a colour change during thermoregulatory sweat testing indicates hypohidrosis, and further tests may be required to localize the lesion.

Magnetic resonance imaging of the brain and ⁄ or spinal cord is the best modality for evaluation when the lesion is suspected to be localized to the central nervous system.

Skin biopsies are useful when anhidrosis occurs as part of a dermatological disorder. Biopsy results may reveal the sweat gland destruction, necrosis or fibrosis, in addition to the findings of the primary dermatological disorder.

Drug-induced fever is a symptom of an adverse drug reaction wherein the administration of drugs intended to help a patient causes a hypermetabolic state resulting in fever. The drug may interfere with heat dissipation peripherally, increase the rate of metabolism, evoke a cellular or humoral immune response, mimic endogenous pyrogen, or damage tissues.

Chronic critical illness is a disease state which affects intensive care patients who have survived an initial insult but remain dependent on intensive care for a protracted period, neither dying nor recovering. The most characteristic clinical feature is a prolonged requirement for mechanical ventilation. Other features include profound weakness associated with critical illness polyneuropathy, increased susceptibility to infection, metabolic changes and hormonal changes. There may be protracted or permanent delirium, or other marked cognitive impairment. The physical and psychological symptoms of the disease are very severe, including a propensity to develop post traumatic stress syndrome.

Strict definitions of chronic critical illness vary. One definition is the requirement for mechanical ventilation for 21 days or more. It is estimated that 5-10% of patients who require mechanical ventilation as part of their initial illness will go on to develop chronic critical illness. Overall prevalence has been estimated at 34.4 per 100 000 of the population. Most adult patients do not survive chronic critical illness, and furthermore even those who are discharged from hospital frequently die soon after discharge. One-year mortality in adults is 48-68%. However, children fare better with two-thirds surviving to 5 years or beyond.

The cause is the most mysterious aspect of the disease. Commentators then and now put much blame on the generally poor sanitation, sewage and contaminated water supplies of the time, which might have harboured the source of infection. The first outbreak at the end of the Wars of the Roses means that it may have been brought over from France by the French mercenaries whom Henry VII used to gain the English throne. However, the "Croyland Chronicle" mentions that Thomas Stanley, 1st Earl of Derby used the "sweating sickness" as an excuse not to join with Richard III's army prior to the Battle of Bosworth.

Relapsing fever has been proposed as a possible cause. This disease, which is spread by ticks and lice, occurs most often during the summer months, as did the original sweating sickness. However, relapsing fever is marked by a prominent black scab at the site of the tick bite and a subsequent skin rash.

Noting symptom overlap with hantavirus pulmonary syndrome, several scientists proposed an unknown hantavirus as the cause. A critique of this hypothesis included the argument that, whereas sweating sickness was thought to be transmitted from human to human, hantaviruses are rarely spread in this way. However, infection via human-to-human contact has been proven in hantavirus outbreaks in Argentina.