Broad-Spectrum Sunscreens Provide Better Protection from the Suppression of the Elicitation Phase of Delayed-Type Hypersensitivity Response in Humans

Abstract

It is well established that ultraviolet radiation has immunomodulatory effects that may be involved in skin cancer. Recent studies have shown that ultraviolet A radiation (320-400 nm) as well as ultraviolet B (290-320 nm) is immunosuppressive. This means sunscreens that mainly absorb ultraviolet B (protection against erythema) may be less effective in preventing ultraviolet radiation-induced immunosuppression than broad-spectrum products. We have studied the effects of ultraviolet A exposure on the human delayed-type hypersensitivity response and compared the efficacy of sunscreens having different levels of ultraviolet A protection under both solar-simulated radiation and outdoor real-life solar exposure conditions. Delayed-type hypersensitivity was assessed using recall antigens. In a first study, two groups of volunteers were exposed to ultraviolet A (either full spectrum ultraviolet A or ultraviolet A1) without prior application of sunscreen and they were shown to exhibit significantly reduced delayed-type hypersensitivity responses. In order to compare the efficacy of sunscreens in preventing photoimmunosuppression, three groups of subjects received 10 cumulative exposures to solar-simulated radiation; one group was exposed unprotected and the other two were exposed after being applied either a ultraviolet B or a broad-spectrum sunscreen, each with the same sun protection factor 9, but with different ultraviolet A protection factors 9 and 2. Then, an outdoor study was conducted in which delayed-type hypersensitivity was assessed before and after six daily exposures. Two different groups of subjects were treated with one of two sunscreens having the same sun protection factor 25 but different ultraviolet A-protection factors. In unprotected volunteers, responses to delayed-type hypersensitivity tests were significantly reduced irrespective of ultraviolet exposure conditions (full spectrum ultraviolet A, ultraviolet A1, solar-simulated radiation). The ultraviolet B sunscreen failed to protect from solar- simulated radiation-induced immunosuppression. In contrast, the broad-spectrum sunscreen having the same sun protection factor but providing high protection in the ultraviolet A range significantly reduced local ultraviolet-induced immunosuppression and prevented the distal effects. In the outdoor study, as compared with delayed-type hypersensitivity responses obtained before sun exposure, no alteration of immune response was detected when the skin was protected by broad-spectrum sunscreen sun protection factor 25 and ultraviolet A-protection factor 14. Conversely, a broad-spectrum sunscreen sun protection factor 25 ultraviolet A-protection factor 6 failed to protect against the sun-impaired response. The above studies clearly demonstrate the role of ultraviolet A in the induction of photoimmunosuppression together with the need for sunscreen products providing efficient photoprotection throughout the entire ultraviolet spectrum.

Measurement of Sunscreen Immune Protection Factors in Humans: A Consensus Paper

“…Apart from their names and concentrations, actives such as antioxidants should be noted as these may influence UVR-induced immunosuppression. Sunscreen absorption spectra should be determined spectrophotometrically in vitro, using either a Transpore tape (3M, Reuil, Malmaison, France) (Diffey and Robson, 1989) or a roughened quartz plate (Moyal and Fourtanier, 2001) as a substrate. Such spectral data enable the calculation of different in vitro factors such as SPF and critical wavelength (l c ) (Diffey, 1994).…”

“…The IPF of a sunscreen has been evaluated using the induction or elicitation arm of the local CHS or DTH response (see Table I), and the systemic DTH response (Moyal and Fourtanier, 2001).…”

Photoprotection

“…Immune protection factor is assessed by the ability of sunscreens to inhibit SSR-induced suppression of the induction arm of local contact hypersensitivity response, or the elicitation phase of delayed hypersensitivity response to recall antigens. 123,125 Immune protection factor has a better correlation with the UVA protectiveness of sunscreen than with the SPF. [122][123][124][125][126][127] At the time of this writing, a consensus statement on this topic is being developed.…”

The suppressive effects of ultraviolet radiation on immunity in the skin and internal organs: Implications for autoimmunity

“…Both UVB and UVA suppress memory recall CHS responses to nickel [7] and DTH responses to PPD [8] in humans. Sunscreen studies have confirmed that outdoor exposure to UVA within natural sunlight suppresses DTH to common microbial antigens [9].…”