UVB light therapy is a common tool used by dermatologists to manage chronic inflammatory skin conditions like psoriasis and eczema. This therapy involves exposing the skin to specific wavelengths of ultraviolet B (UVB) light to suppress the overactive immune response. While effective for clearing skin lesions, the use of ultraviolet radiation raises concerns regarding the potential for long-term skin cancer development. Understanding the mechanisms and clinical data surrounding this risk is important for patients considering this treatment.
Understanding Different Types of UV Radiation
Ultraviolet (UV) radiation is categorized by wavelength, with different types penetrating the skin to varying depths. UVA radiation has a longer wavelength, penetrating deeper into the dermis, and is associated with premature aging and certain skin cancers. UVB radiation has a shorter wavelength, limiting its penetration primarily to the epidermis.
Therapeutic UVB is delivered in two forms: Broadband UVB (BB-UVB) and Narrowband UVB (NB-UVB). BB-UVB uses a wider range of the UVB spectrum (280 to 320 nanometers). NB-UVB, the modern standard, uses a much narrower, focused band, generally centered around 311 nanometers. This restricted wavelength maximizes therapeutic benefit while reducing potentially harmful components.
The Mechanism of UVB Interaction with Skin Cells
The therapeutic effect of UVB light stems from its ability to penetrate and interact directly with the DNA in keratinocytes, the primary cell type of the epidermis. This interaction causes direct damage, primarily cyclobutane pyrimidine dimers (CPDs), where adjacent DNA bases are chemically linked. In conditions like psoriasis, this DNA damage suppresses rapid cell proliferation, which reduces inflammation and slows the disease process.
The formation of CPDs is also the initial step in photocarcinogenesis. Skin cells possess sophisticated DNA repair mechanisms that constantly work to correct UV damage. If damage overwhelms the cell’s repair capabilities and the cell survives, the resulting DNA mutations can lead to malignant transformation over time. Careful control of the light dose is essential to stimulate the therapeutic effect without exceeding the skin’s repair capacity.
Clinical Evidence: Assessing the Long-Term Cancer Risk
Historical data from older phototherapies, particularly Psoralen plus UVA (PUVA), showed a clear, dose-dependent increase in the risk of non-melanoma skin cancers, specifically squamous cell carcinoma (SCC). This context is important because NB-UVB was developed partly to offer a safer alternative. Multiple long-term epidemiological studies have since been conducted to evaluate the cancer risk specifically associated with NB-UVB.
Many studies have concluded that NB-UVB phototherapy does not carry a significant increase in the risk of basal cell carcinoma (BCC), SCC, or melanoma compared to the general population. This suggests that NB-UVB is a safe modality when administered correctly. However, some large cohort studies, such as one conducted in Finland, have shown an increased incidence of BCC, SCC, and cutaneous melanoma among patients treated with Narrowband UVB. These findings highlight that the risk may become apparent only after decades of follow-up or in patients with a high cumulative lifetime dose, often exceeding 300 to 500 total treatments.
It is generally accepted that the risk is significantly lower than that associated with PUVA, and the benefits for patients with severe, debilitating skin diseases often outweigh the minimal long-term risk. The risk appears to be heavily influenced by a patient’s natural skin type and their total cumulative UV exposure. Dermatologists must balance the necessity of treatment with the careful monitoring of a patient’s lifetime exposure record.
Safety Protocols for Minimizing Risk During Treatment
Phototherapy is strictly controlled in a clinical setting by trained professionals. Treatment begins with precise dosimetry, which involves calculating the minimal erythemal dose (MED) or using established protocols based on the patient’s skin type. This ensures the starting dose is just enough to produce a therapeutic effect without causing a burn.
During each session, specific areas of the body that do not require treatment or are highly sensitive are carefully shielded. This includes using protective eyewear to guard the eyes and covering the male genital area, as this skin has been shown to be more susceptible to UV-induced changes. The patient’s skin response is checked before every session, and the dose is adjusted incrementally to maintain efficacy while avoiding excessive redness or burning.
Dermatologists maintain meticulous records of the patient’s cumulative lifetime dose of UV radiation. Regular, ongoing skin surveillance is recommended for patients who have received a high number of phototherapy sessions.