The power of light on living matter

Few contributions have anticipated the challenges of modern medicine with the foresight of Giovan Giacomo Giordano and Leonida Santamaria. In the 1960s, the two researchers laid the foundations of cutaneous photocarcinogenesis. Their experiments demonstrated that oncological risk does not stem solely from solar exposure, but from the complex interaction between light and chemical agents present in the environment.

The milestone was the study published in Nature in 1966: Effects of Light on 3,4-Benzpyrene Carcinogenesis. Santamaria and Giordano proved that 3,4-benzopyrene, a polycyclic aromatic hydrocarbon widespread in cigarette smoke and industrial pollutants, saw its carcinogenic potential enhanced by light. The discovery suggested that toxic substances could be activated by luminous radiation, becoming more harmful to skin cells. Today, we would define this phenomenon as an interaction between components of the exposome.

This research was also a precursor to the modern concept of the tanning factor. In an era when tanned skin was considered a symbol of health, the two scientists helped clarify that pigmentation is primarily a biological defense response to luminous aggression. Tanning is therefore not a mere aesthetic phenomenon: it signals the activation of melanogenesis and cellular mechanisms called upon to limit damage, without, however, nullifying it. Their vision anticipated the overcoming of the "healthy" tan myth and modern dermatological prevention.

In 1968, Giovan Giacomo Giordano consolidated these insights with a review published in the journal Tumori, dedicated to the role of sunlight in human carcinogenesis. He analyzed the incidence of tumors in photoexposed areas, correlating it with the intensity of ultraviolet rays, atmospheric conditions, and individual susceptibility. He formulated a bold hypothesis: photodynamism would not be limited to UV rays alone, but could involve longer wavelengths. Today we know that light can generate reactive oxygen species, alter DNA, and influence repair systems as well as gene expression.

Rereading those works today allows us to grasp their prophetic character. Before "exposome" and "One Health" entered scientific language, Santamaria and Giordano had already outlined a medicine capable of jointly considering environment, chemical agents, radiation, and biological vulnerability. Skin health appeared as the result of a dynamic equilibrium between the organism and the ecosystem.

Celebrating these figures means recognizing the value of research born with limited means and an extraordinary capacity for observation.

For the writer, this recognition also possesses a personal dimension: Giovan Giacomo Giordano was my father. Rereading his work means discovering not only the value of a scientist, but the intellectual and human legacy he left behind. However, it is the rigor of the insights shared with Leonida Santamaria that still speaks to contemporary medicine, reminding us that prevention means understanding the invisible relationships between light, environment, and biology.

Editorial by Prof. Antonio Giordano for the column “Medicine - The Highlights” published in Il Mattino.