Solar medicine: Unraveling the biological and therapeutic effects of sunlight

Background: Sunlight has long shaped human health, functioning as both healer and hazard. Its effects span neonatal jaundice therapy, circadian regulation, cardiovascular health, dermatology, and vitamin D metabolism.
Methods: A structured narrative review was conducted with literature from inception to May 2025 using PubMed, Scopus, and Google Scholar. Keywords included “sunlight exposure,” “phototherapy,” “circadian rhythm,” “mental health,” “vitamin D,” “cardiovascular effects,” and “skin protection.” Reference lists of key papers were hand-searched. Peer-reviewed clinical studies, mechanistic research, and consensus guidelines were included; anecdotal and non–peer-reviewed works were excluded.
Findings: Sunlight supports bilirubin clearance in neonates, stabilizes circadian rhythms, improves mood, regulates blood pressure via nitric oxide mediated and independent pathways, and enables vitamin D synthesis essential for skeletal and immune function. Risks include photoaging, cataracts, and cutaneous malignancies, particularly with unprotected or chronic exposure. Balanced strategies such as protective clothing, sunscreen, antioxidants, and individualized recommendations that consider latitude, season, and skin type can help optimize benefits while reducing harm.
Conclusion: Sunlight remains a double-edged force in medicine. When approached judiciously, it enhances physiological balance and psychological well-being; when neglected or overindulged, it endangers health. An integrative framework for “solar medicine,” blending evidence-based protection with context-specific guidance, may refine public health recommendations and restore a more harmonious human relationship with the sun.