Sunscreen Protection of Contact Hypersensitivity Responses from Chronic Solar-Simulated Ultraviolet Irradiation Correlates with the Absorption Spectrum of the Sunscreen

Abstract

This study compares the ability of two ultraviolet (UV) B-absorbing sunscreens, 2-ethylhexyl p-methoxycinnamate (2-EHMC) and 2-ethylhexyl p-aminobenzoate (Padimate O), and two physical sunscreens, microfine titanium dioxide (MTD) and zinc oxide, to protect the skin immune system from chronic (4 weeks) solar-simulated UV irradiation. Mice were exposed to suberythemal doses of UV before assessing local and systemic immunosuppression and tolerance to a contact sensitizer. Using a UV protocol that induced local but not systemic immunosuppression or tolerance in BALB/c mice, it was shown that Padimate O made the immunosuppression worse, whereas 2-EHMC and MTD protected the immune system. When the cumulative dose was increased by 12.7%, causing systemic immunosuppression and tolerance, none of the sunscreens protected from immunosuppression, but 2-EHMC provided partial, and MTD gave complete protection from tolerance. To examine this apparent lack of protection from systemic immunosuppression, C3H/HeJ mice were used. These mice had a minimal erythema dose similar to that of the BALB/c mice but were systemically immunosuppressed, with only 44% of the UV dose required to immunosuppress BALB/c mice. 2-EHMC provided some protection, whereas MTD provided complete protection from systemic immunosuppression in C3H/HeJ mice. Hence, sunscreens can protect from local and systemic immunosuppression, although this protection is limited and is not related to the sun protection factor of the sunscreens or the minimal erythema dose of the mouse strain. Instead, protection seems to be related to the sunscreens' having a broad absorption spectrum.

Broad-spectrum sunscreens provide better protection from solar ultraviolet–simulated radiation and natural sunlight–induced immunosuppression in human beings

“…[11][12][13][14][15][16] The degree of immune protection reported varies greatly. A recent study 21 using elicitation of contact hypersensitivity to nickel in allergic participants shown that the level of immunoprotection afforded by sunscreens is directly correlated to the level of UVA protection assessed by the persistent pigment darkening method.…”

“…12 The level of protection provided by a sunscreen may depend not only on SPF but also on its absorption spectrum and in particular its absorbing potency in the UVA range. [13][14][15][16] The purpose of our study was to assess in human participants the effects of exposure either to solarsimulated radiation (SSR) or to UVA alone (either fullspectrum UVA [320-400 nm] or UVA-1 [340-400 nm]) or to real outdoor sunlight on the elicitation phase of DTH skin response to recall antigens (Multitest, Pasteur/Mérieux, France) and the efficacy of sunscreens in preventing these effects.…”

Photoprotection

“…101 Sunscreen was reported to prevent UV-induced development of skin cancer in mice by decreasing the formation of cyclobutane pyrimidine dimers; it can also prevent other UV-induced immunologic effects such as epidermal Langerhans call depletion, 115 and suppression of contact hypersensitivity and DTH. 1,24,[116][117][118][119] One study found that broadspectrum sunscreen could prevent UV inhibition of contact hypersensitivity to nickel in human beings. 16 A study in human beings showed that application of sunscreen with SPF 30 before UVB exposure could prevent the decrease in the number of Langerhans cells in the irradiated site, and attenuate the UVinduced suppression of contact hypersensitivity to dinitrochlorobenzene.…”

UV‐induced immune suppression and sunscreen

“…Interaction between sunscreens and the skin Bestak et al (65) reported that a physical sunscreen provided better protection against UV-induced suppression of CHS. Sunscreens could protect local or systemic suppression of CHS.…”