Researchers from the Universitat Politècnica de València, the Francesc de Borja University Hospital in Gandia and the La Ribera University Hospital, through the Fisabio Foundation, have found that sunlight passing through windows in homes is neither a safe nor a recommended alternative for preventing or treating neonatal jaundice, a condition affecting more than half of all newborns.

Neonatal jaundice is usually mild and temporary, but in some cases, it can reach dangerous levels if not treated in time. To avoid complications such as neurological damage, clinical practice relies on early diagnosis and the use of controlled phototherapy devices that emit light within a specific range and at a well-defined intensity.

However, in everyday practice, it remains common to informally recommend "putting the baby in the sun, near the window". Although guidelines do not recommend exposure to sunlight, this practice remains common for preventing or treating jaundice.

In their study, the research team analysed how sunlight behaves as it passes through different types of glass commonly found in homes – up to seven types in total. They concluded that although light entering through windows maintains a high intensity in the blue spectrum – the one used in medical treatments – it does so uncontrolled and is accompanied by potentially harmful radiation.

The researchers measured solar irradiance under different conditions and found that, outdoors, blue light can reach levels up to eight times higher than those used in intensive phototherapy.

"When passing through glass, between 70% and 90% of that light still reaches the interior, which means that a newborn exposed near a window can be exposed to very high levels of radiation that are difficult to control," notes Jesús Alba, a researcher at the Gandia campus of the Universitat Politècnica de València and author of the study.

Furthermore, the study reveals that standard glass does not effectively filter other types of radiation, such as ultraviolet (UVA) and infrared radiation. This can pose an added risk, as these forms of radiation offer no therapeutic benefits and can cause overheating, dehydration or damage to the skin and eyes.

Unlike medical devices, which allow the dose to be adjusted and protect the patient, sun exposure depends on multiple variables, such as time of day, weather, home orientation, and distance from the window.

"This lack of control makes it impossible to guarantee either the efficacy or the safety of this practice. Residential glazing allows very high levels of solar irradiance to pass through, with a broad spectrum that includes UVA and infrared radiation, and blue irradiance several times higher than that used in phototherapy, but without selectivity or dose control. For this reason, exposure to sunlight through a window should not be used as a preventive or therapeutic method to treat neonatal jaundice," emphasises José Miguel Sequí Canet, a paediatrician at the Hospital Francesc de Borja in Gandia

The study concludes by highlighting the importance of following established clinical guidelines, including bilirubin screening and regulated phototherapy when necessary.

The idea for the project and this study arose from Safor Salut, a cooperation programme between key players in the Valencian health innovation system in the La Safor region and its surroundings (UPV, Fisabio and FAES). It has been developed under the 2023 call for proposals of the Polisabio programme – promoted by the UPV and Fisabio – and is part of UniSalut, the collaborative alliance between the Fisabio Foundation and the Valencian universities (UPV, UJI, UMH and, most recently, CEU Cardenal Herrera).

Sequí-Canet JM, Alba Fernández J, Del Rey R, Angelats Romero CM, et al. Luz solar a través de los acristalamientos del domicilio y prevención de la ictericia neonatal. Anales de Pediatría. 2026. doi:10.1016/j.anpedi.2026.504206