Nocturnal hyperhidrosis, commonly known as night sweats, is the frustrating experience of waking up drenched in perspiration. This is distinct from simply overheating due to a warm room or heavy blankets. True night sweats are characterized by drenching perspiration that occurs regardless of a cool sleeping environment. While many instances are linked to manageable environmental or lifestyle factors, persistent episodes can signal an underlying physiological issue.
How the Body Regulates Temperature During Sleep
The body’s internal thermostat, the hypothalamus, orchestrates a slight drop in core body temperature as part of the natural circadian rhythm. This temperature reduction, typically beginning in the evening, helps facilitate the onset and maintenance of sleep. The body attempts to cool itself primarily through distal vasodilation, which involves widening blood vessels in the hands and feet to release heat to the environment.
The brain works to keep the body within the thermoneutral zone, the narrow range of ambient temperatures where the body does not need to expend energy to heat or cool itself. During sleep, the body’s ability to respond to heat and cold becomes less efficient, particularly during the rapid eye movement (REM) phase. Disruptions to this cooling process or shifts in the thermoneutral zone can trigger an exaggerated sweating response, leading to overheating.
External Factors That Increase Body Heat
The most immediate and controllable causes of nocturnal hyperthermia involve the sleeping environment and pre-sleep habits that elevate the metabolic rate. A bedroom temperature above the recommended range of 60 to 67 degrees Fahrenheit can quickly overwhelm the body’s natural cooling mechanisms. The material used for bedding and sleepwear also plays a significant role in heat retention. Synthetic fabrics like polyester trap moisture and heat, preventing evaporative cooling, while natural, breathable fibers wick moisture away.
Consuming alcohol close to bedtime is a common trigger because it initially causes blood vessels near the skin’s surface to dilate, simulating a heat-loss response that leads to sweating. Similarly, spicy foods containing capsaicin stimulate nerve receptors and cause peripheral vasodilation, which the body interprets as overheating. Physical exercise performed too close to sleep onset raises the body’s core temperature through metabolic heat generation. This interferes with the necessary temperature drop required for sleep.
Hormonal Changes and Medication Side Effects
Hormonal fluctuations are primary drivers of night sweats. For women, the transition through perimenopause and menopause is the most common physiological cause, affecting approximately 75 to 85 percent of individuals in this stage. Declining levels of estrogen and progesterone narrow the thermoneutral zone, making the hypothalamus overly sensitive to minor temperature changes. This hypersensitivity causes the brain to mistakenly initiate an aggressive cooling response, resulting in a hot flash or night sweat.
Endocrine disorders also disrupt temperature regulation, most notably hyperthyroidism, or an overactive thyroid. The excess production of thyroid hormones accelerates the body’s metabolism, generating more internal heat and leading to chronic sweating. Nocturnal hypoglycemia, where blood sugar levels drop too low, prompts the body to release stress hormones like adrenaline and cortisol. These hormones activate the sympathetic nervous system, which triggers sweating as a counter-regulatory measure to raise blood sugar.
Prescription medications can interfere with the central nervous system’s thermal regulation or stimulate the sweat glands directly. Several drug classes have been linked to night sweats, including:
- Selective serotonin reuptake inhibitor (SSRI) antidepressants (e.g., sertraline and escitalopram).
- Hormone therapy medications.
- Certain blood pressure drugs.
- Nonsteroidal anti-inflammatory drugs (NSAIDs) like aspirin, which can cause excessive perspiration as the body cools after breaking a fever.
Specific Underlying Health Conditions
Persistent night sweats can be a symptom of specific chronic health issues. Obstructive sleep apnea (OSA), characterized by repeated pauses in breathing, is frequently associated with nocturnal hyperhidrosis. The increased effort required to breathe against an obstructed airway, combined with fluctuations in oxygen and carbon dioxide levels, activates the sympathetic nervous system, causing profuse sweating.
Infections often manifest with night sweats as the body’s immune system releases inflammatory signaling molecules called cytokines. Tuberculosis is historically known to present with drenching night sweats, but other infections like endocarditis and HIV can also cause this symptom. Primary hyperhidrosis involves excessive sweating unrelated to core body temperature, affecting both day and night, and is not related to temperature regulation.
Anxiety activates the body’s “fight or flight” response, which increases heart rate and blood flow, leading to heat generation and sympathetic nervous system-driven sweating. While rare, night sweats can be an early, non-specific symptom of certain cancers, such as lymphoma or leukemia, where the immune response generates fever and subsequent sweating.
Signs That Require Medical Evaluation
Occasional night sweats are common, but certain accompanying signs require a medical evaluation. Consult a healthcare provider if the sweating occurs regularly, is severe enough to consistently soak through clothing or bedding, or significantly disrupts sleep quality. Immediate attention is warranted if the night sweats are accompanied by other unexplained symptoms, such as:
- Unintentional and significant weight loss.
- A persistent low-grade fever.
- Unexplained pain or a chronic cough.
- Symptom onset coinciding with starting a new medication.
- Hot flashes continuing long after the typical end of the menopausal period.