Therapeutic hypothermia has revolutionized the care of infants born with hypoxic-ischemic encephalopathy, reducing death and major neurodisability by cooling the body to 33–34°C for 72 hours. The treatment works by slowing metabolic demand and blunting the cascade of oxidative stress and inflammation that follows oxygen deprivation. But the very fat that insulates a newborn—especially the brown fat deposits across the back, shoulders, and cheeks—is exquisitely vulnerable to cold injury. When the body is cooled, blood flow to fat depots can falter, and when rewarming begins, a reperfusion-type injury can trigger crystallization of triglycerides within fat cells, setting off a granulomatous inflammatory reaction. The resultant SCFN is often self-limited but harbors a sinister secret: the granulomas express vitamin D receptors and can activate vitamin D outside the kidneys, causing uncontrolled hypercalcemia that can peak weeks after the skin lesions resolve, leading to renal failure, cardiac arrhythmias, and brain injury if missed.

Walsh and colleagues set out to quantify the burden of this complication in a contemporary cohort of cooled newborns across several regional centers, capturing data on more than five hundred consecutive therapeutic hypothermia cases. Their analysis pegged the incidence of SCFN at roughly 6.4%—far from a rare event, yet strikingly variable across institutions, likely reflecting differences in cooling protocols, skin surveillance, and diagnostic thresholds. Crucially, the study mapped a constellation of risk factors that could help clinicians stratify newborns from the moment they are wrapped in cooling blankets. Infants with lower birth weight and those who experienced more profound acidosis at birth were significantly more likely to develop SCFN, as were those who required longer durations of temperature management or who had therapeutic hypothermia initiated after a longer delay from the sentinel event. The location of fat necrosis favored the back and the posterior neck, exactly the regions in direct contact with the cooling mattress, underscoring the mechanical contribution of pressure and conductive cold transfer.

The team also dissected the biochemical follow-up, revealing that among affected infants, nearly one in three developed hypercalcemia requiring medical intervention, with serum calcium levels sometimes soaring above 14 mg/dL weeks after the skin findings had resolved. The pathophysiological clock, it turns out, ticks silently. As the inflammatory granulomas mature, they ramp up extrarenal production of 1,25-dihydroxyvitamin D, driving intestinal calcium absorption and bone resorption. The delayed timing of this metabolic storm means that a baby can be discharged healthy only to return to the emergency department with failure to thrive, irritability, and dangerously high calcium. Clinicians who are unaware of the link may chase parathyroid hormone levels and vitamin D metabolites without ever examining the newborn’s skin for subtle, healing SCFN plaques, which may have flattened and faded by then.

A particularly intriguing finding was that the use of active versus passive cooling devices modulated risk, with servo-controlled systems that more precisely maintain target temperature associated with a modest reduction in fat necrosis rates compared with older, less regulated approaches. This hints that not just the absolute temperature but the stability and gradient of cooling matter at the tissue level. The brown adipose tissue in neonates, rich in saturated fatty acids with high melting points, is primed to crystallize when the local microenvironment drops even a few degrees below the core temperature, especially when combined with pressure-induced ischemia. The new data reinforce the notion that meticulous positioning and the use of soft barriers between the cooling source and the skin could be more than just nursing comfort—they may be a neuroprotective adjuvant in their own right, preventing a cascade that leads to hypercalcemic crises.

While the study is retrospective, it is by far the most comprehensive regional effort to characterize SCFN in the hypothermia era, including detailed chart reviews and long-term follow-up data. The authors argue for a standardized screening protocol: weekly calcium monitoring for the first two months of life in any cooled newborn, with heightened vigilance for those with low birth weight, severe metabolic acidosis at admission, and visible skin changes. Dermatology consultation and ultrasound can help distinguish SCFN from sclerema neonatorum or bacterial cellulitis, but the real urgency is biochemical. Simple blood tests, if timed correctly, can catch the calcium climb before kidneys calcify.

The viral message from this research is one of hidden danger and simple intervention. A treatment that saves brains can inadvertently prime a metabolic trap that threatens kidneys and hearts, but the trap is detectable with a routine blood draw and manageable with hydration, loop diuretics, and, in refractory cases, bisphosphonates or corticosteroids. The paper is already circulating through neonatology social media groups, with bedside clinicians sharing their own photographs of SCFN plaques and emphasizing that every cooling center needs a dedicated follow-up pathway. As therapeutic hypothermia expands to lower-resource settings worldwide, the need to understand this complication becomes only more acute—because without surveillance, a baby who survived a low-oxygen birth could succumb to a hidden calcium flood weeks later.

The study also lays the groundwork for future preventive trials. Could adjusting the rewarming rate, or applying intermittent breaks in mattress contact, reduce the incidence without compromising neuroprotection? Might genetic variations in fatty acid metabolism or the vitamin D axis predispose certain infants? The research opens these questions while giving neonatal units an immediate, actionable risk calculator. As the senior author noted in presenting the findings, “We have entered an era where we can no longer cool and forget.” For thousands of families whose newborns undergo therapeutic hypothermia each year, that shift in mindset will mean the difference between a complication caught early and a crisis that arrives at home, unseen and unmeasured.

Subject of Research: Incidence and risk factor profile for subcutaneous fat necrosis among newborns undergoing therapeutic hypothermia

Article Title: Incidence and risk factor profile for subcutaneous fat necrosis among newborns undergoing therapeutic hypothermia: a multi-center regional cohort

Article References: Walsh, B.H., El-Shibiny, H., Cherkerzian, S. et al. Incidence and risk factor profile for subcutaneous fat necrosis among newborns undergoing therapeutic hypothermia: a multi-center regional cohort. J Perinatol (2026). https://doi.org/10.1038/s41372-026-02772-0

Image Credits: AI Generated

DOI: 10.1038/s41372-026-02772-0

Keywords: subcutaneous fat necrosis, therapeutic hypothermia, neonates, hypoxic-ischemic encephalopathy, hypercalcemia, incidence, risk factors, neonatal intensive care, brown adipose tissue, cooling therapy