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People with bipolar disorder often experience dramatic shifts in mood, energy, and behavior. A new study suggests that these psychological states may have physical signatures as well. Researchers found that individuals going through manic episodes tend to have higher skin temperatures during the day compared to both healthy individuals and those with bipolar disorder in stable or depressive states. Once the manic episode subsides, the elevated temperature appears to return to baseline. The findings were published in the Journal of Affective Disorders and suggest skin temperature may serve as a digital signal of mood changes.
Bipolar disorder is a chronic mental health condition characterized by alternating periods of depression and mania. Depressive episodes are marked by sadness, low energy, and hopelessness, while manic episodes are associated with elevated mood, impulsivity, and increased activity levels. The disorder affects about 2.4 percent of the population and is one of the leading causes of disability worldwide.
Diagnosing and monitoring bipolar disorder currently relies almost entirely on interviews and symptom reports, which can be subjective and vary widely between individuals. This limitation has driven interest in identifying physiological markers that might objectively reflect changes in mood states.
“Psychiatry has historically relied on subjective assessments – patient reports, clinical observations, and symptom checklists – while other medical specialties have benefited from objective laboratory tests and imaging. This creates significant challenges in making accurate diagnoses and treatment decisions, especially when patients’ memories may be unreliable or their insight limited during acute episodes,” said study author Diego Hidalgo-Mazzei, a senior psychiatrist and postdoctoral researcher at the Hospital Clínic de Barcelona.
“The emergence of wearable technology offers an unprecedented opportunity to continuously and objectively capture physiological signals that may correlate with mental health states. Our team at the INTREPIBD-TIMEBASE project is exploring how these digital biomarkers – including activity patterns, electrodermal activity, heart rate variability, and now skin temperature – might help us better understand and monitor severe mental conditions like bipolar disorder. Temperature regulation particularly intrigued us because previous research suggested thermoregulatory abnormalities in mood disorders, but no one had examined this specifically during manic episodes using modern wearable devices.”
The researchers enrolled 139 adults, including 104 patients diagnosed with bipolar disorder and 35 healthy controls, in their study. The patients were grouped based on their clinical state: depressive episode, manic episode, or stable mood (a state known as euthymia). Participants experiencing either a depressive or manic episode were assessed twice—once during the acute episode and again after their symptoms had remitted. Those in the euthymic group and the healthy controls were assessed only once.
Participants wore a wrist-mounted device called the E4 wristband for approximately 48 hours. This wearable tracked their skin temperature as well as their movement. The device recorded skin temperature using an infrared sensor, and researchers extracted average temperature data in short intervals. Because skin temperature can be influenced by many factors, the researchers also took into account potential confounders such as age, sex, time of day, level of physical movement, season, and use of medications that can interfere with body temperature regulation.
The most notable finding was that individuals undergoing manic episodes had consistently higher skin temperatures during the daytime compared to all other groups. On average, their skin temperature was 33.61 degrees Celsius during waking hours, which was approximately 0.8 degrees higher than the euthymic group and significantly higher than the depressive and control groups. Importantly, once the manic symptoms subsided, the elevated temperature decreased as well, dropping to an average of 33.21 degrees Celsius—no longer significantly different from the other groups.
“Our research found that people experiencing manic episodes of bipolar disorder have measurably higher skin temperature during waking hours – about 0.8°C higher than those in stable mood states,” Hidalgo-Mazzei told PsyPost. “Importantly, this temperature elevation returns to normal once the manic episode resolves, suggesting it’s directly linked to the mood state rather than being a permanent characteristic.”
“This matters because it demonstrates that mood episodes have real, measurable physiological manifestations that we can track objectively using simple wearable devices. While a temperature change alone isn’t enough to diagnose or monitor bipolar disorder, combining it with other digital biomarkers could eventually help patients and clinicians detect early warning signs of mood episodes and track treatment response more accurately.”
All groups showed the expected circadian rhythm of skin temperature: lower values during the day and higher values at night. However, the group with mania exhibited higher daytime skin temperatures across most hours, from mid-morning through evening. While the depression group showed a slight earlier rise in temperature in the evening compared to others, this pattern was not statistically significant.
The researchers also examined the range of daily temperature changes, or amplitude, for each group. No meaningful differences were found in amplitude or distribution, further supporting the idea that only the overall temperature level—not the pattern of fluctuation—was affected during mania.
“Two findings particularly stood out,” Hidalgo-Mazzei said. “First, we expected to see temperature changes in depressive episodes based on previous literature, but found no significant differences. This suggests that the thermoregulatory changes in mania and depression may involve different mechanisms. Second, the temperature increases during mania disappeared completely after symptom remission, showing it’s truly state-dependent. This was not expected and extremely interesting. This clean on-off pattern was more pronounced than we anticipated and reinforces the potential value of temperature as a state marker rather than a trait marker of bipolar disorder.”
The researchers offer several possible explanations for why skin temperature might increase during manic episodes. One theory centers on mitochondrial activity. Mania has been associated with increased mitochondrial energy production, which leads to greater heat generation in the body. This excess heat could be dissipated through the skin, resulting in higher peripheral temperatures. Some studies have reported elevated oxygen consumption and mitochondrial activation during manic states, which aligns with this hypothesis, though other research has suggested reduced respiratory capacity during both mania and depression.
Another possibility involves disruptions in brain systems that regulate temperature. For example, the hypothalamus and brainstem circuits are known to play roles in both mood and thermoregulation. Abnormalities in serotonin or orexin signaling, both of which influence temperature control, have also been documented in bipolar disorder. Additionally, alterations in the circadian system, especially in the suprachiasmatic nucleus, could disrupt normal patterns of vasodilation and vasoconstriction, affecting heat loss through the skin.
The study also references work in pediatric populations with a “fear of harm” phenotype linked to altered temperature gradients during sleep. Although more severe and less common, this condition could share biological pathways with adult mania.
While the findings are suggestive, the authors caution that skin temperature alone is unlikely to serve as a reliable standalone marker for mania. “Several important limitations should be noted,” Hidalgo-Mazzei told PsyPost. “The effect size was relatively small, and skin temperature is highly variable – influenced by environmental factors, physical activity, medications, and individual differences. We measured wrist temperature, which is more reactive but less stable than core body temperature.”
“Our sample sizes were modest, and groups differed in age distribution. We also couldn’t fully account for factors like anxiety or agitation that often accompany mood episodes and might independently affect temperature. Most critically, while these findings are scientifically interesting, the temperature changes alone aren’t large or specific enough for clinical use – we need larger studies combining multiple biomarkers to develop clinically useful tools.”
“In general, it might also be interesting to discriminate if the physiological patterns we are finding are a secondary signal of the stress produced by the mood state or rather a primary pattern of the disorder per se,” Hidalgo-Mazzei continued. “For instance, we are now extending the wearables monitoring to other disorders and specifically through a new project (DIREKT) exploring physiological markers of response in MDD patients undergoing esketamine treatment.”
“Our ultimate goal is to develop a multimodal monitoring system that combines temperature with other digital biomarkers like activity patterns, heart rate variability, and electrodermal activity to create personalized “digital signatures” of mood episodes. This requires much larger samples and more sophisticated analyses to identify patterns that generalize across individuals.”
“We envision a future where patients with bipolar and other disorders could wear devices that learn their unique physiological patterns and provide early warnings of impending mood episodes, similar to how continuous glucose monitors have transformed diabetes management and promptly act upon them,” Hidalgo-Mazzei added. “In parallel, clinicians to have at the office individual validated objective-continuous data that could help supporting shared-decision making with the patients, and/or assess treatment response together among other use-cases. However, reaching this goal will require extensive validation studies, regulatory approval, and careful integration into clinical workflows.”
“This research represents a small but important step toward more objective, continuous monitoring of mental health conditions. While we’re excited about the potential of digital biomarkers, it’s crucial to remember that technology will complement, not replace, the therapeutic relationship and clinical expertise. We’re particularly grateful to all the participants who wore devices during some of their most challenging moments. Their contribution is helping us build a more objective understanding of bipolar disorder that could benefit millions of people worldwide.”
“The full TIMEBASE-INTREPIBD study continues to collect data on multiple physiological signals, and we encourage interested readers to learn more about our broader research program at https://intrepibd.github.io/. The research team includes collaborators from the University of Barcelona, King’s College London, Deakin University, and the University of Edinburgh, representing the interdisciplinary nature of digital psychiatry research.”
The study, “State-dependent skin temperature increase during manic episodes of bipolar disorder,” was authored by Clàudia Valenzuela-Pascual, Rocío G. Lamberti, Ariadna Mas, Roger Borràs, Gerard Anmella, Filippo Corponi, Vincenzo Oliva, Michele De Prisco, Marta Korniyenko, Marina Garriga, Meritxell González-Campos, Marc Valentí, Isabella Pacchiarotti, Antoni Benabarre, Iria Grande, Anna Bastidas, Isabel Agasi, Cristina Romero-Lopez-Alberca, Cecilia Muñoz-Doña, Ana Catalan, Allan H. Young, Michael Berk, Eduard Vieta, and Diego Hidalgo-Mazzei.
