According to various studies, for anywhere from 20 to 50 percent of patients hyperhidrosis represents a genetic condition that is not linked to any underlying medical condition. It seems like Asians and Jewish people have a much greater rate of prevalence for hyperhidrosis than other races. No wonder that the world's most experienced ETS surgeon, Chien-Chi Lin, is based in Taiwan, and is responsible for the major innovations in ETS surgical technique in recent years. Israel, which has a majority Jewish population, accounts for a relatively high number of ETS surgeries every year even though it has a small population. Several of the most experienced surgeons in the US also initially learned to perform sympathectomy in Israel. For most people who have primary hyperhidrosis, the condition starts in puberty. Hyperhidrosis in children who have not reached puberty should not be treated with surgery, since it can sometimes diminish with time.
For some, the sweating is caused by secondary hyperhidrosis, which means that there is an underlying medical condition causing perspiration. Often, secondary hyperhidrosis causes excessive sweating all over the body (generalized) rather than in localized regions such as the palms/feet/face/armpits. The most cited medical condition that can cause hyperhidrosis is hyperthyroidism. Other possibilities include adrenal gland tumors or dysfunctions, hyperpituitarism, and spinal cord injuries. Temporary hyperhidrosis can occur from all kinds of medical and life conditions ranging from angina to menopause, as well as from side effects from taking medications such as propranolol, physostigmine, pilocarpine, antidepressants, and selective serotonin reuptake inhibitors.
For the remaining hyperhidrosis sufferers, there is no known genetic or medical condition related explanation. I fall under this category it seems. Posters on various internet discussions have postulated a number of theories to explain the development of hyperhidrosis and/or facial blushing in this group, ranging from excessive parental and/or peer pressure and/or bullying during childhood, to excessive pressure on the back near the sympathetic nerves via wearing heavy backpacks in childhood, to too much competitive sports in childhood, to swimming a lot in chlorinated water, and much more.
Surprisingly, localized hyperhidrosis (as most visiting this site probably suffer from) is not due to nervousness, excess heat and humidity, or obesity as would be expected. Those conditions can make the problem worse sometimes, but do not cause localized hyperhidrosis. People with palmar hyperhidrosis experience it for hours at a stretch even if they are skinny and in an air conditioned room by themselves with no reason to be nervous or stressed. Its just a very strange problem that does not seem to have an evolutionary benefit or explanation. Why do humans even have the majority of their sweat glands in the hands and feet?