We recently received two question about night sweats, or nocturnal hyperhidrosis through our consultation email service and I thought a blog might be the best way to address what we know currently about night sweats and to get some comments from the field.
Most people associate night sweats with menopause and that may be one of the most common causes of nocturnal hyperhidrosis. However, men get night sweats as well and the prevalence increases as we age for a variety of reasons. The regulation of sweating is complex and involves both thermoregulatoy and non-thermoregulatory mechanisms in the brain and body. At its simplest, sweating helps to reduce the core body temperature when it rises above certain thresholds called the thermo-neutral zone (TNZ). Sweating occurs when threshold levels in core body temperatures trigger a hypothalamic response and this can occur because it’s hot outside or because core body temperature rises due to exercise. The TNZ naturally fluctuates on a circadian rhythm and your body is normally cooling over the course of the night with your lowest temperature and lowest sweat threshold occurring a few hours before you naturally wake up. Therefore, if you are warm during the evening and your body wants to be cooling, you are more likely to sweat.
Now, it is important to differentiate night sweats from occasionally being sweaty at night, usually for an environmental reason. You may occasionally awaken after perspiring excessively, particularly if you are sleeping under too many blankets or if your bedroom is too warm. However, these types of episodes are typically not labeled as “night sweats” and do not represent a medical problem. While there has not been an agreed upon conference on defining night sweats, generally they are defined as a recurrent (more nights than not), drenching sweating during the night that requires: no changing of clothes (mild), sleep disturbed by need to arise and wash face or affected body areas, but no clothing change required (moderate) or requiring changing of bed clothes or bedding (severe). In sleep medicine, night sweats are most often considered to be a miscellaneous secondary parasomnia. Primary parasominias are those due to disorders of sleep per se and secondary parasomnias are those that result from dysfunction in other organ systems, but like to express themselves at night in particular.
It is interesting that so little is published about night sweats and that it is not something that gets talked about in public a lot. However, among patients specifically queried in the offices of primary care physicians, as many as 41% report having experienced night sweats in the prior month (Mold, 2006) and one study noted that questions about the cause of night sweats are one of the most frequent questions posed by patients and one for which, physicians say, they struggle to provide an evidence based answer for (Ely et al, 1997). It should also be noted that as many as 30% of adults over the age of 64 complain of night sweats.
There are many different causes of night sweats and to find the cause a physician will often need to take a detailed medical history and run some lab tests to determine if a medical condition is the underlying cause of the night sweats. Some of the conditions that are known to cause night sweats include:
There is some evidence that the onset of night sweats could be a weak predictor of early progression to AIDS in a person with HIV. Very low testosterone levels in men, called andropause when related to aging, can result in night sweats as well. Low blood sugar or hypoglycemia can cause night sweats and people taking insulin or other oral diabetes medications may experience nighttime hypoglycemia and sweating. Hormone disorders such as carcinoid syndrome and hyperthyroidism can cause sweating of flushing especially at night. Neurologic conditions such as spinal syringomyelia, stroke and autonomic neuropathy (autonomic seizures) can occasionally cause night sweats. Additionally, night sweats can be an early symptom of some cancers, the most common type is lymphoma (though usually this occurs with other symptoms such as unexplained weight loss and fever). Certain medications can also lead to night sweats. Antidepressants are a common medication that can lead to night sweats with as many as 22% of people taking antidepressants reporting night sweats as a side effect (especially sertraline and venlafaxine). Hormone replacement therapy (HRT) medications may also induce night sweats as a side effect. Other medications have also been associated with night sweats such as aspirin and acetaminophen, though not at significant rates and likely not caused by the medication, but by the condition they are treating i.e., influenza. Finally, some foods especially spicy foods like chili peppers and excessive garlic can cause sweating at night. Also hot drinks, excessive sugar, caffeine and alcohol can lead to night sweats.
One thing that often comes up is the relationship between night sweats and PTSD or trauma nightmares. While there is no literature specifically addressing its prevalence, sweating at night remains a common complaint of people with PTSD. There is also no objective empirical evidence of a specific relationship, more likely both PTSD and nightmares may cause some patients to wake up and because of the autonomically arousing nature of these conditions the patient may report being excessively sweaty or to notice and report being sweaty. Anecdotal evidence and case studies suggest that the problem resolves when the trauma is successfully treated.
Night sweats are also associated with several sleep symptoms though the nature of the association is remains unclear. Maybe the night sweats are caused by the sleep problem, like restless leg syndrome or periodic limb movements or perhaps patients who wake up in the night because of sleep issues are simply more likely to notice and complain of nights sweats or it could be that the sleep problem and the night sweats are caused by a third factor like depression, PTSD or medications. The most common comorbid sleep condition associated with night sweats is obstructive sleep apnea. Regardless, a history of night sweats should prompt the clinician to ask more questions about sleep.
Regarding evaluation, a number of medical evaluation approaches to night sweats have been proposed over the years however there are no published studies regarding the accuracy or cost-effectiveness of these protocols. The most common approach is a thorough medical history and lab work to identify any potential underlying medical or psychiatric condition.
Finally, there are very few published studies that have examined symptomatic treatment of night sweats, except in postmenopausal women. A few case studies suggest the use of alpha adrenergic blockers such as benztropine, terazosin or clonidine to reduce night sweats in those taking an SSRI. Thioridazine or thalidomide may be effective for patients with terminal cancer and desloratadine may help for narcotic addiction related night sweats for those receiving methadone treatment. All of the currently existing studies though are too small and underpowered to yield reliable conclusions according to a recent systematic review of the literature (Mold et al, 2012).
The good news is that nocturnal hyperhidrosis is not associated with adverse health outcomes when you control for the underlying medical conditions mortality. In other words, night sweats may result in increased daytime fatigue, insomnia and stress, but night sweats themselves are not imminently deadly. The first line of defense is to identify and treat any potential underlying cause. Additionally, there are some tips that might help reduce or alleviate night sweats.
Dr. Bill Brim is the Deputy Director of the Center for Deployment Psychology.