Hy*per*hi*dro*sis Excessive or profuse sweating. SYN hyperephidrosis, hyperidrosis, polyhidrosis, polyidrosis, sudorrhea from Stedman's Medical Dictionary.

Hyperhidrosis, also known as excessive sweating, is a medical condition. There is no single cause of it. Because it is not a disease, it can be a symptom of another medical condition such as a disorder of the nerves. For some people, there may be no explainable cause for their excessive sweating, and they may be considered to have a medical condition known as essential (idiopathic or primary) hyperhidrosis. This may be due to over activity of the nerves that send signals to the sweat glands in the skin, the sympathetic nervous system. Sometimes this idiopathic form of hyperhidrosis can be genetically transmitted, and it often runs in families; this form may first show up in early childhood. Other people may have sweating as a symptom of known medical conditions, such as an overactive thyroid gland (hyperthyroidism), from nerve damage due to diabetes (autonomic dysfunction) or spinal cord injuries, with psychiatric disorders such as panic attacks or anxiety disorders, or even due to the hot flashes associated with menopause. Many people who have hyperhidrosis may also have reddening of the skin, which is most noticeable in the face as blushing, due to the same nerve over-activity. Some medications may by themselves cause excessive sweating, such as the medications often used for prostate cancer, AIDS, or pyridostigmine (Mestinon™) used for the condition myasthenia gravis.

Sweating is a normal bodily function that serves to cool off the skin and lubricate the skin (especially in areas that may rub against other areas of skin, such as under the arms, under the breasts, and between the legs). Special microscopic glands (sweat glands) in the deep layer of the skin, the dermis, make sweat by filtering fluid and salts out of the blood, and secreting this fluid up through small tubes in the skin, the sweat ducts, that empty out into small pores at the top layer of the skin, the stratum corneum (Wenzel FG & Horn TD, Nonneoplastic disorder of the eccrine glands, J. Am Acad Dermatol. 1998 38:1-17). Some areas of the skin have many sweat glands, while other areas have relatively few; they are present in the highest concentration in the palms and soles. In addition to sweat glands, skin also has oil glands that surround almost every hair root, the sebaceous glands. Finally in some areas, such as the underarm and the groin, are found a special, unusual sweat gland called an apocrine gland, which secretes a very thick type of sweat that has a large amount of fatty chemicals in it. These chemicals can be broken down by bacteria on the surface of the skin to create the smelly chemicals that are mostly responsible for body odor. These glands can occasionally get diseased or infected, and may lead to a condition known as hidradenitis suppurativa, which is a serious medical condition that may require antibiotics or surgery to cure the disorder.

Two different sets of nerves supply these many glands, the sympathetic nerves, which tend to increase sweating when one is excited, nervous, or afraid (the "fight or flight response"), and the parasympathetic nerves, which tend to decrease sweating of the skin. At the ends of the nerves, the body releases special chemicals called neurotransmitters, which carry the electrical signal from the nerves onto the cells near the nerve endings. For the sweat glands, the chemical at the tips of the sympathetic nerves is acetylcholine; too much of this chemical present next to the sweat glands stimulates them to produce large amounts of fluid. Many doctors feel that one of the biggest problems in people with idiopathic hyperhidrosis is the fact that the sympathetic nerves are over stimulated, making the neurotransmitters "go haywire" at the nerve endings. Many activities that stimulate the nervous system, such as strong smells, spicy foods, increased air temperatures, exercise, high emotional excitement, stress or nervousness may cause attacks of excessive sweating through sympathetic nerve over activity.

In order to decrease sweating, one has to either cut down the nerve impulses to the sweat glands, cut down on the acetylcholine, destroy the glands, or block off their ducts, so that the sweat cannot flow out onto the skin. One main way to cut down sweating is to use a medicine on the surface of the skin to cause the sweat to thicken and plug up the ducts, which is how the antiperspirants that are often used under the arms to decrease underarm sweat and odor work. These usually contain aluminum metal salts, such as aluminum chloride, which have to be frequently reapplied, or else the clumps in the ducts will get dissolved, unblocking the ducts and permitting sweating.

The sweat glands themselves can be destroyed, but since they are so small and numerous, and are located deep in the skin, methods such as electrolysis (which uses electric currents to destroy the hair roots) are not very practical. If only a special area of the skin, such as the underarms, cause sweating problems, there have been some reports on the use of liposuction to remove the apocrine sweat glands there (Rowland Payne C & Doe PT, Liposuction for axillary hyperhidrosis, Clinical and Experimental Dermatology 1998, 23:9-10).

Electric currents through the skin, iontophoresis, may disrupt the function of the sweat glands, preventing them from working for a long time. With the use of a home operated machine, a small electric current is sent through the skin from one area to another. The electric current "shocks" the sweat glands, and they stop making sweat until they recover. By using this machine regularly, a few times a week, prolonged dryness in the area of treatment can be obtained, that can last for weeks. This may work well if only a few small areas of skin have the excessive sweating problem, but requires frequent treatments. The nervous supply to the sweat glands can be interrupted by cutting or destroying the sympathetic nerves. Since these nerves are extremely small, they are usually reached at areas near the spinal cord, where many nerves run together into structures known as sympathetic ganglia, before they spread out throughout the body. Once the nerves are cut or destroyed, the sweat glands that are supplied by those nerves stop secreting sweat; in addition, other parts of the skin also lose their sympathetic nerve supply, so the skin may lose its ability to control its temperature and blood flow. This may lead to paleness and coldness of the skin where its nerve supply has been disrupted. People who suffer from blushing may find this side effect desirable, as they will lose the ability to blush in those areas affected by the surgery. Medication may be taken internally that works to block the neurotransmitter, acetylcholine, from stimulating the sweat glands. Some of the more useful medications include the anticholinergics (such as glycopyrrolate or atropine), some antihistamines, some antidepressants, and some of the tranquilizers. However, these medications will also affect other parts of the body, and may lead to possible side effects, including dry mouth, drying of other secretions, constipation, or other side effects. One new approach that may work on small areas of skin that have excessive sweating is to inject botulinum toxin (Botox®) into small areas of the skin (such as the underarms), which blocks the acetylcholine for up to a few months before it wears off .

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