HX22 Shining a light on dermatology

Abstract Phototherapy has been a cornerstone of dermatological treatment, evolving from ancient practices into a sophisticated medical intervention. Around 2000 Bce in Egypt, patients with vitiligo applied juice extracted from Ammi majus to affected skin and exposed it to sunlight. This plant contains bergapten and methoxsalen, psoralen derivatives with photosensitizing properties. Although the mechanisms were unknown at the time, the use of sunlight, or heliotherapy, laid the foundation for exploring light as a therapeutic tool. The modern era of phototherapy began in the late 19th century with Danish physician Niels Ryberg Finsen, who developed a concentrated ultraviolet (UV) radiation treatment for lupus vulgaris, a skin manifestation of tuberculosis. His success with UV radiation earned him the Nobel Prize in 1903 and is considered the birth of modern phototherapy. Finsen’s groundbreaking work validated the therapeutic potential of light and marked a significant milestone in dermatology. In the early 20th century UVB therapy became a cornerstone for treating psoriasis, eczema and vitiligo by regulating immune responses and promoting healing. The introduction of narrowband (NB)-UVB therapy in the 1980s refined this approach, offering more targeted treatment with fewer side-effects compared with broad-spectrum UVB. Alongside UVB therapy, psoralen combined with UVA (PUVA) therapy emerged as an effective option for severe cases of psoriasis and other inflammatory skin conditions. However, concerns regarding PUVA’s long-term risks, including skin ageing and cancer, led to safer alternatives like NB-UVB therapy. A significant advancement in phototherapy came with photodynamic therapy (PDT), which combines photosensitizing agents with light to treat skin cancers and precancerous lesions. The foundations of PDT were laid in 1900 when German medical student Oscar Raab discovered the phototoxic effects of certain dyes, such as acridine, when exposed to light and oxygen. Since then, PDT has evolved into a noninvasive alternative to surgery, effectively targeting abnormal cells while preserving healthy tissue. In the late 20th century, lasers introduced new precision in phototherapy, enabling targeted treatment for vascular lesions, acne scars and pigmentation disorders. Light-emitting diodes offered noninvasive options for indications such as acne, wound healing and skin rejuvenation, becoming popular for their accessibility and minimal side-effects. Today, phototherapy remains integral to dermatological care, continually advancing through research into optimized wavelengths, personalized approaches and integration with systemic therapies. From its origins in heliotherapy to cutting-edge technologies, phototherapy’s history reflects a profound and enduring quest to harness the healing power of light. This journey underscores its vital role in both the past and future of dermatology.