Your body will lose its ability to sweat above the nipple line when you have the surgery to stop hand sweating. Some surgeons forget to mention this. I got this side effect after my ETS surgery in 1998, but it has luckily not affected me adversely as far as my upper body becoming overheated when I play sports or otherwise. I do feel like my scalp is dry sometimes (see best dandruff shampoo choices), but perhaps that has nothing to do with my not sweating in that area. Some people have complained of a very dry face and scalp after ETS surgery. A few people have had major body temperature changes (thermoregulatory disturbances) after surgery during times of stress, and they have theorized this to be a result of an altered body "thermostat" that cannot enable heat loss via sweating through the upper body after surgery. I have been lucky and do not suffer from any of these problems.
Edit: Since around the mid-2000s, many surgeons have been cutting the lower T-3 and/or T-4 ganglions for palmar hyperhidrosis instead of the T-2 ganglion, and it seems like this side effect of upper body anhidrosis will not usually occur with the new surgery. However, some surgeons believe that cutting T-3 and/or T-4 to cure excessive hand sweating problems might lead to a higher likelihood of re-occurrence of palmar sweating, but the vast majority still seems to prefer this risk over cutting T-2.
ETS reduces the resting heart rate in a fraction of patients -- this fraction has been listed anywhere from one-tenth to well over one-half depending on which surgeon you listen to. My resting heart rate fell by around ten percent after my ETS surgery in 1998, according to surgery documents. Although probably not dangerous, this is something to keep in mind (and you should ask your surgeon about this if he/she forgets to mention it). Are you willing to mess with your heart rate to get rid of consistently sweaty palms? I would still say yes based on my terribly sweaty palms. The reason ETS reduces your heart rate is because some of the upper thoracic ganglions in the sympathetic chain have direct and/or indirect connections to the heart. It should be noted that the parasympathetic nervous system (the opposite of the sympathetic nervous system) also affects the heart rate. The sympathetic nervous system will raise your heart rate when you are in danger, and the parasympathetic nervous system lowers your heart rate.
Some surgeons are now warning that if you are an athlete, ETS might reduce your peak performance due to this side effect, but other surgeons say that ETS has no effect on your maximum heart rate. For me, a slightly lower heart rate does not seem to have made any difference in athletic ability. My resting heart rate is never lower than 60 beats per minute, which is the cutoff point for bradycardia. Usually, problems can only arise if your heart rate falls below 50 beats per minute. Also, some surgeons have suggested that a slightly lower heart rate is good for you in the long run. Interestingly, many excellent athletes such as cyclists Lance Armstrong and Miguel Indurain have an excessively low resting heart rate of around 30 beats per minute. For most adults, resting heart rates fall between 60 and 80 beats per minute.
ETS leads to compensatory sweating (a better term is reflex sweating per Dr. Chien-Chi Lin) in almost 100 percent of patients according to some surgeons. In the past, most surgeons usually estimated a figure of around 40-60 percent, but this figure has steadily increased as more and more patients have started getting compensatory hyperhidrosis a year or two after surgery and the surgeons have realized that the problem does not necessarily start the day after the surgery (especially if the surgery is performed in winter and a patient is thus unable to experience compensatory sweating at its worst immediately).
Edit: In 2009, Dr. Timo Telaranta from Finland e-mailed me and said that his current surgical technique guarantees no compensatory sweating. I remain skeptical, especially since the techniques have kept changing slightly every few years during the past decade, and this has essentially allowed surgeons to get away without explaining some of the side effects and problems associated with what they were doing a few years ago. i.e., they are able to always say that "the new technique won't cause those same problems."
The palms and feet house most of the body's sweat glands, so it seems logical to infer that stopping sweating at either place will almost always guarantee compensatory sweating elsewhere. For me, the compensatory sweating occurred in my feet instead of in my chest or back or thigh areas as is most common. See next paragraph for more on that.
Your feet sweating (aka plantar hyperhidrosis) can become much worse than before surgery. Most people with palmar hyperhidrosis also have plantar hyperhidrosis. Surgeons typically say that there is anywhere from a 50-95 percent (again, depending on which of them you listen to) chance of a reduction in feet sweating after ETS for palmar sweating (i.e., a bonus benefit). The feet sweating will remain the same as before ETS in the remaining patients according to the surgeons. However, I have experienced significantly greater feet sweating post ETS and so have many others I have communicated with or read about online. I haven't seen a single surgeon point out this possibility to date. Sweat signals to the feet generally come from the lumbar sympathetic chain in your lower back, so it seems that in some patients, the lumbar sympathetic chain starts transmitting more sweat signals to the feet once palmar sweating has ceased as a result of the destruction of part of the sympathetic (thoracic) nervous system. A lumbar sympathectomy can possibly cause reverse ejaculation in men and urinary incontinence in women (among other side effects), so almost no surgeon offers this procedure for the purposes of curing feet sweating anymore. Edit: As of 2008/2009, it seems like lumbar sympathectomy is becoming fashionable again, although only one surgeon in the US currently offers it. I would hold off on getting this surgery until more results come in, and I would recommend trying iontophoresis on your feet if you have not already done so.
Edit: In May 2009, I finally got rid of my excess feet sweating using Hidrex iontophoresis. You must attempt iontophoresis therapy before looking into getting endoscopic thoracic sympathectomy surgery!
You can get extremely cold hands post ETS, and like some of the other side effects, this can show up a year or more after the surgery (so this side effect conveniently doesn't show up in most surgeons' list of potential side effects that is often based on surveys conducted in the immediate aftermath of surgery). This is also why ETS is not performed to cure Raynaud's (cold hands) syndrome by many surgeons anymore, since initially warm hands post-ETS can become extremely cold a year or two down the road. According to an e-mail to me from the pioneers of the endoscopic method of sympathectomy, Dr. Goran Claes and Dr. Christopher Drott, this severely cold hands side effect happened in two percent of their patients due to "increased sensitivity to surrounding catecholamines". I get this side effect once in a while, and it seems to be positively correlated to stress levels and cold weather.
After ETS, some patients (typically less than five percent in the case of ETS for palmar sweating according to most surgeons) experience a recurrence of their original symptoms. This recurrence is usually most common with regards to ETS for facial blushing, for Raynaud's Syndrome and for other such non-hyperhidrosis related problems. In my own case, I had some right had sweating return a year or so after ETS while the left hand has always remained extremely dry. During intense exercise, my right hand can get very sweaty at times. It is unclear to the surgeons why this recurrence occurs, and some claim that there is no way a destroyed ganglion can regenerate, so the sweat signals must be transmitting via other pathways. Many patients need to get re-operated upon if the recurrence is significant. I am not sure how the re-operation works if the destroyed ganglion has not regenerated and hope to hear from someone with this knowledge. Does the surgeon destroy other ganglions besides the dead T-2 (or T-3 in newer procedures) in the event of recurrence? What happens to surrounding scar tissue from the initial operation?
The only side effects that surgeons have discussed honestly and have quoted consistent risk percentages for are Horner's Syndrome (droopy eyelids) and Gustatory Sweating. Gustatory sweating (GS) is significant forehead sweating when eating or even smelling spicy food and can occur a year or two after ETS. Horner's Syndrome is extremely rare in the hands of an experienced surgeon, since it requires damage to the stellate ganglion (T-1). The few patients who do get permanent Horner's Syndrome have had to get cosmetic surgery to normalize their appearance. Gustatory Sweating occurs in anywhere from 10-20 percent of patients, although it is unclear if this figure is higher in the long run. I got the gustatory sweating side effect a year or two after surgery, but only when eating very spicy food, which I unfortunately enjoy. It is quite strange that I am unable to sweat at all from my forehead after having had endoscopic thoracic sympathectomy even while exercising during 100 degree Fahrenheit temperatures, but sweat profusely from there when eating very spicy food.
Edit 2013: In recent years, I have actually looked forward to getting GS. I miss the sensation of not being able to sweat on my forehead when playing sports or when exerting myself in other ways, so when I eat very spicy food and get the sweat rolling, I derive pleasure from it. I feel normal, and imagine that I am getting rid of waste via the sweat (although I do not think that is scientifically true).
Problems that can occur during surgery include pneumothorax, intercostal neuralgia and even death on very rare occasions (it seems like around ten deaths have occurred in Western countries as a result of ETS surgeries). Pneumothorax is some level of lung collapse after the operation. Intercostal Neuralgia is local pain in the chest wall area. Persistent or severe pain is unusual.
There are a host of other side effects that some people have complained about that are possible due to ETS such as sensitivity to light, dizziness, blood pressure changes, dry scalp, hair loss etc... If enough people complain about a specific problem and at least a few surgeons verify the problem as a side effect of ETS (as has been the case for all the side effects I listed above), I can add the problem in the above list. Otherwise, I am treating those rumored side effects as unrelated to ETS.
Curiously, people who have severe facial blushing also get the second thoracic ganglion destroyed just as most palmar and facial hyperhidrosis patients still do (although many surgeons now cut T-3 and/or T-4 to treat palmar hyperhidrosis). It seems that significant types of upper body innervation arise from the thoracic cavity and its associated ganglions, especially T-1 and T-2.
Many people make a very fast decision to have ETS. A quick 1-hour (half an hour each side) minor surgical procedure that often doesn't even require overnight stay sounds miraculous. However, this surgery can sometimes lead to long-term turmoil on the internal networking of your body. After all, there must be an evolutionary reason as to why the sympathetic nerve chain is in a location where it can never be damaged unlike virtually all other components of your body. Humans can easily damage external parts of their bodies through physical injury. In addition, most internal organs such as the brain, heart, kidney, liver, and lung can be damaged by cancer, diet, drinking, smoking and the like. However, to my knowledge, the sympathetic nervous system (or more specifically, the thoracic ganglions) can almost never be physically damaged without surgical intervention because it is deep inside the chest and made up in a rope like manner that cannot break easily. A bad diet, smoking, drinking and so on can also not damage the sympathetic nervous system.
Having said all that, ETS is a last resort option that is almost a surefire cure for your palmar (and facial if present at the same time) hyperhidrosis. However, I firmly believe that there is an extremely strong chance of curing hyperhidrosis using one or a combination of the numerous alternative methods available that are outlined on this website and discussed on the hyperhidrosis forum. So long as you are persistent.
If you have read all the above, but have already had hyperhidrosis surgery, I hope I have not made you become a hypochondriac who starts imagining that every possible physical problem you have is due to sympathetic nervous system destruction. Some medical problems and negative changes to your body could be part of aging or part of your genetic destiny. There are several sites out there that blame ETS surgery for every possible medical condition on earth, and these sites are even more damaging than the surgeons' sites that make it sound like ETS is an easy and obvious answer to your sweating problems.
Moreover, I have talked with a few happy people who had open surgical sympathectomy many decades ago to cure hyperhidrosis, and they had numerous ganglions removed along with major bleeding and other significant trauma during and after surgery. These people are enjoying their life and old age despite the side effects they had to deal with all their lives. In the end, willpower can often overcome most side effects.
Update: June 26, 2023
In a recent NY Times article about excessive sweating, the reader comments are especially interesting. I am pasting the screenshot of my favorite one below. This reader had both cervical and lumbar sympathectomies for his/her hand and feet sweating almost 50 years ago. Insane that in her 70s she is still interested in the subject and posting an online newspaper comment. A cervical sympathecomy is even higher up than a thoracic sympathectomy. Perhaps they sometimes used to do the former decades ago for hyperhidrosis? Or this reviewer just got an incorrect name given to him/her? In any case, this just shows that you can live a normal life even decades after a highly invasive open sympathectomy with major and numerous ganglion destruction.
Check out the portion of the website where I discuss the evolution of ETS surgery and confusion regarding ETS techniques and the way surgeons have managed to personalize their own variety of ETS (sometimes for marketing purposes) -- i.e., cutting different ganglions for hand sweating relative to other surgeons, emphasizing/deemphasizing kuntz nerve search and destruction, cutting the ganglion above or below each level or completely cutting it, "microcutting" versus clamping versus electro-coagulation versus removing and so on.