non-UV phototherapy

In neonatal jaundice, unconjugated (indirect) bilirubin accumulates because the newborn liver has immature UDP-glucuronosyltransferase activity, risking kernicterus if levels become excessive. Phototherapy uses blue-green light (wavelength ~450-460 nm, near the absorption peak of bilirubin) rather than ultraviolet light, distinguishing it from UV-based treatments used in dermatology (e.g., PUVA, narrowband UVB for psoriasis/vitiligo). The mechanism involves three photochemical reactions: (1) configurational (geometric) isomerization of bilirubin from the toxic 4Z,15Z form to the less toxic, more water-soluble 4Z,15E form, which is reversible and excreted in bile; (2) structural isomerization to lumirubin, an irreversible reaction producing a compound that can be excreted in bile and urine without conjugation; and (3) photo-oxidation, a minor pathway producing polar products excreted in urine. Lumirubin formation is the most important mechanism for bilirubin elimination. Because the process occurs in the skin and does not require UV wavelengths, it avoids UV-associated risks such as DNA damage, erythema, and theoretical carcinogenesis, making it safe for neonates. Clinical use includes conventional phototherapy with fluorescent blue lights or LED devices, fiberoptic blankets (Bili-blanket), and intensive phototherapy for severe hyperbilirubinemia. Indications are guided by age-specific bilirubin nomograms (e.g., Bhutani nomogram) factoring in gestational age and risk factors. Side effects include bronze baby syndrome (in cholestatic infants with conjugated hyperbilirubinemia), transient rashes, dehydration, retinal damage (hence eye shielding), and temperature instability. This is distinct from UV phototherapy (UVA, UVB, narrowband UVB, PUVA) used for dermatologic conditions like psoriasis, vitiligo, and atopic dermatitis, which works via immunomodulation and apoptosis of pathogenic T cells in the skin.