Sunlight: Friend or Foe? Evidence-Based Effects on Skin and Health

The session introduces an evidence-based discussion of whether sunlight is a friend or foe, focusing first on its effects on skin and later on systemic benefits and personalized photoprotection. The speaker explains that ultraviolet light is only a small fraction of sunlight reaching Earth, while visible light and infrared make up much more. Although UV is well known for causing erythema, pigment changes, photoaging, and skin cancer, visible light is now recognized as biologically active as well, especially blue light. Studies show that visible light can cause immediate and persistent pigmentation, particularly in darker skin, with Opsin-3 in melanocytes acting as a key sensor and triggering calcium influx, increased melanin production, and reduced autophagy, which prolongs darkening. Visible light combined with UVA1 has a synergistic effect on pigmentation, and shorter visible wavelengths such as blue and green light are most responsible. The presentation also reviews how sunlight contributes to photoaging through UV-induced matrix metalloproteinases and collagen degradation, and notes that darker skin has more natural photoprotection but still experiences some photoaging and carcinogenic risk. The talk concludes by transitioning to the next section on systemic effects of sunlight.