Photosensitizing

Photosensitizing refers to the property of a substance to increase a person’s sensitivity to light, especially ultraviolet or visible wavelengths. When a photosensitizer is present in tissues and light exposure occurs, a chemical reaction can take place that damages cells or triggers an immune response. Photosensitivity reactions are commonly categorized as phototoxic or photoallergic. Phototoxic reactions resemble an exaggerated sunburn and can occur in anyone given sufficient amounts of the agent plus light. Photoallergic reactions involve an immune response and require prior sensitization, often presenting as an eczematous rash rather than a simple sunburn.

In medicine, photosensitizers are used deliberately in photodynamic therapy (PDT) to treat certain cancers, precancerous lesions, and infections. A photosensitizing agent is given systemically or applied locally and accumulates in target tissues. When illuminated with a specific wavelength of light, the agent transfers energy to nearby oxygen, generating reactive species that destroy diseased cells. Common clinical agents include porphyrin- and porphyrin-like compounds, such as those used in PDT, and prodrugs like 5-aminolevulinic acid (5-ALA), which are converted in the body to active photosensitizers. Outside of therapy, many medications can induce photosensitivity, leading to adverse reactions upon light exposure. Examples include certain antibiotics (tetracyclines, fluoroquinolones), sulfonamides, diuretics (thiazides), nonsteroidal anti-inflammatory drugs, and amiodarone, among others. Some natural compounds, notably psoralens found in certain plants, can also enhance light sensitivity.

Management focuses on minimizing light exposure when a photosensitizing agent is present, using protective clothing and broad-spectrum sunscreen, and following medical guidance regarding dosing and timing. Seek medical attention for severe or persistent reactions.