Diaphoresis is the state of perspiring (sweating) profusely; a diaphoretic is something that has the power to cause increased perspiration.
Normal physical causes of diaphoresis include physical exertion, menopause, fever, spicy foods, and high environmental temperature. Strong emotions (anger, fear, anxiety etc.) and remembrance of past trauma can also trigger profuse sweating.
The vast majority of sweat glands in the body are innervated by sympathetic “cholinergic” neurons. Sympathetic postganglionic neurons usually secrete norepinephrine and are named sympathetic adrenergic neurons. However, when sympathetic postganglionic neurons innervate sweat glands they secrete acetylcholine and hence are termed sympathetic “cholinergic” neurons, the only sympathetic postganglionic neurons known to secrete acetylcholine instead of norepinephrine.
Diaphoresis may be associated with some abnormal conditions, such as hyperthyroidism and shock. If it is accompanied by unexplained weight loss or fever or by palpitations, shortness of breath, or chest discomfort, it suggests serious illness.
Diaphoresis is also seen in an acute myocardial infarction (heart attack), from the increased firing of the sympathetic nervous system, and is frequent in serotonin syndrome. Diaphoresis can also be caused by many types of infections, often accompanied by fever and/or chills. Most infections can cause some degree of diaphoresis and it is a very common symptom in some serious infections such as malaria and tuberculosis. In addition, pneumothorax can cause diaphoresis with splinting of the chest wall. Neuroleptic malignant syndrome and other malignant diseases (e.g. leukemias) can also cause diaphoresis.
Diabetics relying on insulin shots or oral medications may have low blood sugar (hypoglycemia), which can also cause diaphoresis.
Drugs (including caffeine, morphine, alcohol, and certain antipsychotics) may be causes, as well as withdrawal from alcohol, benzodiazepines, nonbenzodiazepines or narcotic painkiller dependencies. Sympathetic nervous system stimulants such as cocaine and amphetamines have also been associated with diaphoresis. Diaphoresis due to ectopic catecholamine is a classic symptom of a pheochromocytoma, a rare tumor of the adrenal gland. Acetylcholinesterase inhibitors (e.g. some insecticides) also cause contraction of sweat gland smooth muscle leading to diaphoresis.
Mercury is well known for its use as a diaphoretic, and was widely used in the 19th and early 20th century by physicians to “purge” the body of an illness. However, due to the high toxicity of mercury, secondary symptoms would manifest which were erroneously attributed to the former disease which was being treated with mercurials.
Infantile acrodynia (childhood mercury poisoning) is characterized by excessive perspiration. A clinician should immediately consider acrodynia in an afebrile child who is sweating profusely.