Introduction
Waking up drenched in sweat, even when your bedroom is cool, can be an unsettling experience. These episodes, known as night sweats, are different from normal perspiration from being too warm in bed. Night sweats are defined as repeated, excessive sweating during sleep that is not related to your environment and can be so severe that it soaks your clothes and bedding, leaving you uncomfortable and sometimes even chilled.[2]
So, why does your body sometimes overheat and sweat profusely while you’re asleep? The reasons range from harmless lifestyle triggers to underlying medical conditions that warrant a doctor’s attention.
Hormonal Shifts
One of the most common causes of night sweats, particularly in women, is a fluctuation in hormone levels. Hormones play a crucial role in regulating your body’s internal thermostat, located in the hypothalamus in your brain.[3] When these hormones fluctuate, your body’s temperature control can go haywire.
- Menopause and Perimenopause: Roughly 80% of women experience hot flashes and night sweats as their estrogen levels begin to decline.[4, 5] The drop in estrogen makes the hypothalamus hypersensitive to even minor temperature changes, sometimes as small as 0.8°F, triggering an exaggerated cooling response and resulting in a sudden burst of sweat.[5]
- Other Hormonal Changes: Night sweats are also common during pregnancy due to fluctuations in estrogen and progesterone.[6] Additionally, hormonal imbalances from conditions like hyperthyroidism (an overactive thyroid) can speed up your metabolism and cause excessive sweating and heat intolerance.
- Medications: Certain drugs can also affect hormonal balance or interfere with your nervous system’s temperature regulation. Common culprits include antidepressants (especially SSRIs), opioids, steroids, and some hormone therapies.[9, 10] If your sweating started after beginning a new medication, it is worth discussing with your doctor.[11]
The Role of Infections, Cancers, and Sleep Disorders
While many causes of night sweats are benign, persistent sweating can be a symptom of a more serious underlying health issue.
- Infections: Night sweats are a classic symptom of certain infections, such as tuberculosis (TB), endocarditis, or abscesses.[2] The sweating is often part of the body’s systemic immune response to fight the infection, which can trigger a fever and subsequent sweating as the fever breaks.[13]
- Cancers: Persistent night sweats can be an early symptom of some cancers, particularly lymphoma and leukemia.[14, 15, 16] In lymphoma, night sweats are part of a group of symptoms called “B symptoms,” which also include fever and unexplained weight loss.[14, 17] The sweating is believed to be caused by chemicals released by the cancer cells or the body’s immune reaction to them.[17]
- Sleep Disorders: People with obstructive sleep apnea (OSA) are up to three times more likely to experience night sweats than those without it.[18, 19] The repeated pauses in breathing and the physical stress this puts on the body can cause an increase in core temperature, leading to a sudden sweat burst as the body struggles to cool down.[18]
Environmental and Lifestyle Triggers
Sometimes, the explanation for night sweats is much more straightforward and can be easily prevented.
- Bedroom Environment: A bedroom that is too warm, or heavy bedding and pajamas made from synthetic materials, can trap heat and cause you to overheat. What feels like a medical “night sweat” may simply be preventable overheating.
- Diet and Substances: Consuming alcohol, caffeine, or spicy foods in the hours before bed can elevate your body temperature and trigger a sweating response.[15] Nicotine is also a known stimulant that can cause night sweats.[11]
- Anxiety and Stress: Your mental state doesn’t fully turn off at night. High levels of stress or anxiety can activate your sympathetic nervous system (the same “fight-or-flight” response that makes your palms sweat during the day) and this physiological reaction can carry over into your sleep.[21]
Idiopathic Hyperhidrosis
In some cases, there is no clear cause for the sweating. A condition called idiopathic hyperhidrosis is diagnosed when the body produces excessive sweat, day or night, without any known underlying medical reason.[22, 23] It is thought to be caused by overactive nerves that stimulate the sweat glands, even without the presence of heat or physical activity.[24]
When to See a Doctor
A single episode of night sweats is generally not a cause for alarm. However, you should talk to your doctor if:
- Night sweats occur often enough to disrupt your sleep or daily life.
- They are accompanied by other symptoms such as unexplained weight loss, persistent fever, pain, or a chronic cough.[15]
- The sweats started suddenly without any changes in your environment, medications, or lifestyle.
