V. L. S. Medeiros, MD and H. W. Lim, MD

Department of Dermatology, Henry Ford Hospital, Detroit, MI, USA


Key to the management of photodermatoses is photoprotection, which includes seeking shade; wearing photoprotective clothing, wide brimmed hats, and sunglasses; and applying sunscreens. The process of selecting the most effective sunscreen depends on identification of the wavelengths of photons that are responsible for inducing the sensitivity reaction, which can be determined through assessment of patient history or by phototesting. Sunscreens with sun protection factor (SPF) >30 that incorporate photostable or photostabilized ultraviolet A (UVA) filters (labeled as “broad spectrum” in the US) are usually the appropriate choice for adequate photoprotection.

Key Words:
photodermatoses, photoprotection, photosensitivity disorders, sunscreen, UVA, UVB

Photodermatoses are a group of diseases involving abnormal cutaneous reactions to solar radiation. They include immunologically mediated photosensitive disorders, drug or chemical induced photosensitivity reactions, DNA repair-deficiency photodermatoses, and photoaggravated dermatoses.1 While these diseases have different pathophysiologic mechanisms, not all of which have been clearly defined, photoprotection is an integral part of their management. Photoprotection includes seeking shade, wearing photoprotective clothing, a wide brimmed hat, and sunglasses, as well as applying broad spectrum sunscreens with sun protection factor (SPF) >30.1-3

Choice of Sunscreen Protection

The method by which the clinician chooses the most effective sunscreen for each patient depends on identification of the photon wavelength responsible for inducing the sensitivity reaction, i.e., the action spectrum.3 This can often be ascertained through the determination of minimal erythema dose to ultraviolet B (UVB) (280-320 nm) (MED-B) and ultraviolet A (UVA) (320-400 nm) (MED-A), and though the induction of lesions by UV or visible light (400-700 nm).2,3 The fact that window glass filters out UVB, but not longwave UVA, also helps to determine the action spectrum of the patient’s photosensitivity disorder.

In the United States, UVB and UVA filters are categorized into organic and inorganic filters (Table 1). While there are many excellent UVB filters, there are only a limited number of organic UVA filters available in the US, namely the benzophenones (oxybenzone, dioxybenzone, and sulisobenzone), butyl methoxydibenzoylmethane (commonly known as avobenzone), and methyl anthranilate.1,3 All, with the exception of avobenzone, are primarily protective only against UVA-2 (320-340 nm). The absorption of avobenzone extends into UVA-1 (340-400 nm).1,3 However, because avobenzone is photolabile, degradation occurs rapidly upon exposure to sunlight. In the past few years, technology has been developed to photostabilize avobenone. This can be achieved by combining it with photostable UV filters, such as octocrylene, salicylates, or oxybenzone; in some products non-UV filter photostabilizing compounds, such as diethylhexyl 2,6-naphthalate (DEHN), diethylhexyl syringylidene malonate (Oxynex® ST), or caprylyl glycol are also used.1 Ecamsule (Mexoryl™ SX) is a photostable organic short UVA filter (with maximum absorbance at 344 nm) that was approved by the US FDA in 2006 only as a component of certain sunscreen products.4 The approved inorganic sunscreens or physical blockers are titanium dioxide and zinc oxide, which offer protection from UVB to visible ranges. They are used in micronized form to improve cosmetic acceptability.1,3 However, it should be noted that the micronized form protects only in the UVB and UVA spectrums, but not in the visible range.

The SPF value for sunscreens reflects the ability of the product to protect against UV-induced erythema, which is primarily the effect from UVB exposure, and to a lesser extent from UVA-2. While there are rating systems used in many other countries to grade the protectiveness of sunscreens against UVA, currently, the FDA has not yet finalized the revised rating system that will be implemented in the US. Consumers should look for sunscreens that provide “broad spectrum” protection, which would indicate that the formulations contain UVA filters. However, as noted above, since many UVA filters do not cover longwave UVA (UVA-1), and not all sunscreens incorporate a photostabilized UVA-1 filter (i.e., avobenzone), the current UVA rating system used in the US reveals significant shortcomings.

Sunscreens and Photodermatoses

Herein, the use of sunscreens in the management of photodermatoses (polymorphic light eruption and solar urticaria) and photoaggravated dermatosis (lupus erythematosus) is outlined.

Polymorphic Light Eruption (PMLE)

PMLE is the most common photodermatosis, with prevalence as high as 10-20%, typically starting during the second and third decades of life.1,3,5,6 Lesions develop within hours of sun exposure, usually resolve in a few days, and do not scar. PMLE is generally most severe in the spring or early summer and a genetic predisposition appears to be a likely risk factor.5,6 The pathogenesis is thought to be attributable to the failure of normal UV-induced immunosuppression, which results in enhanced reactivity to UV triggered photoallergens in the skin.1,5,6 Photoprovocation tests have shown that PMLE was induced by UVA in 59% to 94.2% of cases, and UVB in 23% to 40%.6-9 Induction by a combination of UVA and UVB was observed in 18% to 90% of patients, depending on the methodology used in the photoprovocation tests.6,7,9 Because most sunscreens protect predominantly against UVB, and therefore, fail to prevent PMLE,6-9 the need to study sunscreens with high UVA protection, through the use of photostable UVA filters, was fostered.8,9 In a retrospective study of 133 patients with PMLE, the complete follow-up information on photoprotection was available for 79 subjects. The data revealed that the use of a sunscreen with a mean SPF of 14 did not prevent skin lesions in 88% of these patients.7 Another study using a sunscreen with high SPF and high UVA-PF (UVA protection factor), containing photostable UV filters (Tinosob® M, Tinosorb® S) and photostabilized avobenzone, showed that it protected against the development of lesions in 69% of subjects with PMLE after standardized photoprovocation.8

Other trials have compared the efficacy of two sunscreens with similar SPF, but different levels of UVA protection. In an indoor, bilateral comparison study, 14 volunteers used a product with SPF 60 and UVA-PF 15 (containing avobenzone, Mexoryl™ SX, Eusolex®, and micronized titanium dioxide) on one side of the chest, and the other side received another product with SPF 50 and UVA-PF 4 that contained titanium dioxide and zinc oxide. Following photoprovocation, only two subjects developed new PMLE on the side treated with the higher UVA-PF sunscreen, while 14 subjects developed new lesions on the other side.4 In an outdoor study, 16 female subjects susceptible to PMLE were exposed daily to sunlight for 7 days after using two products with similar SPF 60+, but different UVA-PF values on each half of the body. Fifteen subjects experienced eruptions with the photounstable lower UVA protection (UVA-FP 4) product, compared with only four patients exhibiting eruptions with the photostable high UVA (UVA- PF 28) sunscreen.4

Filter Type Name of UV Filter Concentration
Organic UVB Filters Cinnamates Octinoxate (octyl methoxycinnamate, Parsol MCX) 7.5%
Cinoxate 3%
PABA derivatives Para-aminobenzoic acid (PABA) 15% 15%
Padimate O (octyl dimethyl PABA) 8%
Salicylates Octisalate (octyl salicylate) 5%
Homosalate 15%
Trolamine salicylate 12%
Others Octocrylene 10%
Ensulizole (phenylbenzimidazole sulfonic acid) 4%
Organic UVA Filters Benzophenones Oxybenzone (benzophenone-3) 6%
Sulisobenzone (benzophenone-4) 10%
Dioxybenzone (benzophenone-8 3%
Others Butyl methoxydibenzoylmethane (avobenzone, Parsol 1789) 3%
Meradimate (menthyl anthranilate) 5%
Inorganic Filters Titanium dioxide 25%
Zinc oxide 25%
Table 1. Sunscreen active ingredients listed in the US FDA monograph10

Solar Urticaria (SU)

SU is an uncommon photodermatosis, often occurring
in the third decade of life and demonstrating a female
preponderance.9,11,12 Urticaria is a mast cell-mediated
disease that can develop within minutes after exposure to
sunlight.9,11,12 The action spectrum includes UVA, UVB, and
visible light.9

Because there is no sunscreen product available that
adequately protects against visible light, photoprotection
in SU induced by visible light can only be achieved with
physical measures, such as clothing, which in one study
resulted in symptomatic control in 84% of patients.9 Broad
spectrum high SPF sunscreens are helpful for SU that is
triggered by UVA and/or UVB.

Lupus Erythematosus (LE)

LE is the most common photoaggravated dermatosis.13,14 Following UV exposure, skin lesions develop within days or up to weeks after and can persist for months.14 Tumid LE is the most photosensitive subset, followed by subacute cutaneous LE, systemic LE, and discoid LE. Sunlight exposure can even induce systemic disease activity.14 Provocative phototesting by Kuhn et al. produced characteristic skin lesions in 175 of 323 LE patients; 42% were reactive to only UVB and 34% to UVA only.13 Of the patients receiving combination UVA + UVB irradiation, 53% exhibited positive photosensitivity reactions.

The study performed by Stege et al.15 tested the efficacy of three distinct sunscreens to prevent the UV radiation-induced generation of skin lesions in photosensitive LE patients by employing a standard provocative phototest.15 The 11 patients developed LE-specific skin lesions upon photoprovocation with a combination of UVA and UVB radiation. The same group was tested with three different sunscreens. The most effective was a product with high SPF and high UVA-PF (UVB filter: octocrylene; UVA filters: Mexoryl™ SX, Mexoryl™ XL, avobenzone, and titanium dioxide), which protected 11 of 11 patients. Five patients were protected by a product with similar SPF, but medium UVA-PF (UVB filters: Eusolex® 6300, Parsol® MCX, Uvinul® T150, Neohelipan®; UVA filter: avobenzone; titanium dioxide) and only three by a product with the lowest SPF and lowest UVA-PF (UVB filters: Eusolex® 6300, Parsol® MCX, Uvinul® T150; UVA filter: avobenzone; titanium dioxide). While several of the filters used in the study are not commercially available in the US, this trial does indicate that sunscreens with high SPF and high UVA-PF are necessary for the management of patients with photosensitive LE.15


Sunscreens are an integral component of photoprotection in the management of photodermatoses. UV filters are broadly categorized into organic UVB and UVA filters, and inorganic filters. The efficacy of sunscreens has been well documented in PMLE, solar urticaria, and lupus erythematosus.


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