Sun protection factor: meaning and controversies - SciELO

1 An Bras Dermatol. 2011;86(3) Sun protection factor: meaning and controversies *Fator de prote o solar: significado e controv rsiaSergio Schalka1 Vitor Manoel Silva dos Reis2 Abstract: The Sun protection Factor (SPF) is the most important data to quantify the effectiveness of asunscreen, being universally accepted. The method is based on determining the minimum erythema-tous dose (MED), defined as the smallest amount of energy required for triggering the erythema, inareas of protected and unprotected skin. The SPF value is then calculated as the ratio between the MEDof protected and unprotected skin. The first publication of a method for determining the SPF was pre-sented in 1978 by the FDA agency, followed by other publications of FDA and other internationalregulatory agencies. Although considered the reference method for quantification of sunscreen efficacyof topical products, there are controversies in literature about the method for determining the SPF andthe implications of the real conditions of use in the protection achieved in practice by users.

2 Keywords: Dermatology; Solar radiation; Sunscreening agentsResumo:O Fator de Prote o Solar (FPS) o principal dado para quantifica o da efic cia fotoproteto-ra de um filtro solar, sendo universalmente aceito. Seu m todo baseado na determina o da DoseEritematosa M nima (DEM), definida como sendo a menor quantidade de energia necess ria para o des-encadeamento de eritema, em reas de pele protegidas e n o protegidas pelo produto em estudo. Ovalor do FPS , ent o, calculado como a raz o num rica entre a DEM da pele protegida e a da pele n oprotegida. A primeira publica o demonstrando um m todo para determina o do valor do FPS foiapresentada em 1978 pela ag ncia norte-americana FDA, seguida por outras publica es do pr prioFDA e de outras ag ncias regulat rias internacionais. Apesar de ser considerado o m todo refer nciapara quantifica o da efic cia fotoprotetora de produtos t picos, existem controv rsias na literaturaacerca do m todo para determina o do FPS e sobre as implica es das reais condi es de uso na pro-te o atingida na pr tica pelos usu rios.

3 Palavras-chave: Dermatologia; Queimadura solar; Protetores de raios solaresApproved by the Editorial Board and accepted for publication on *Work conducted at a private clinic - Sao Paulo (SP), Brazil. Conflict of interest: None / Conflito de interesse: NenhumFinancial funding: None / Suporte financeiro: in Dermatology - Associate Professor of Dermatology - University of Santo Amaro (UNISA) - Sao Paulo (SP), in Dermatology - Professor of Dermatology, School of Medicine, University of Sao Paulo (FMUSP) - Sao Paulo (SP), Brazil. 2011 by Anais Brasileiros de DermatologiaINTRODUCTIONIt has always been part of human nature toprotect the skin against sunburn through the use ofclothes and accessories or simply by avoiding sunexposure. The first scientific reports on the attempteduse of photoprotective agents emerged in the late XIXcentury, with substances of very limited effect.

4 1In 1891, Friedrich Hammer 1published the firstmonograph on photobiology, in which he discussedthe use of different products in the prevention ofsunburn (1891 apud Roelandts, 12007, ).In 1928, the first sunscreen becomescommercially available in the United States of AmericaREVIEW507An Bras Dermatol. 2011;86(3) an emulsion containing benzyl salicylate and subsequent years, however, littleattention was given to photoprotective agents, andtheir use was very World War II, due to the need foradequate photoprotection of American soldiers inbattle fronts in the tropics, red petrolatum was usedas a standard protective 1943, para-aminobenzoic acid (PABA) waspatented as the first sunscreen established, indicatinga new stage of photoprotection. 2 However, it was only during the 1970s that thepopularity of sunscreens increased with theincorporation of different UVB filters in creams andlotions.

5 3 The use of UVA filters effectively began in 1979,but only the introduction of inorganic particles oftitanium dioxide in 1989 and of zinc oxide in 1992 ledto more effective protection in the UVA range classic definition of a sunscreen, accordingto Pathak4, is a product designed to block the sun andprotect or shelter viable skin cells against thepotentially harmful effects of ultraviolet radiation suchas sunburn and skin to current concepts, topicalphotoprotectors or sunblocks (or sunscreens), aresubstances applied to the skin in differentpresentations which contain in their formulationingredients capable of interfering with sun radiation,reducing its harmful effects. 5 Ultraviolet (UV) filters are the ingredientspresent in sunscreens that have the ability to interactwith incident radiation through three (3) basicmechanisms: reflection, dispersion and absorption, asshown in Figure 1.

6 6UV filters can be divided into inorganic(physical) or organic (chemical) filters, depending ontheir physico-chemical properties. 7 Inorganic filters are metal oxide particlescapable of reflecting or dispersing incident radiationthrough an optical mechanism. Its mainrepresentatives are zinc oxide (ZnO) and titaniumdioxide (TiO2), usually used in combination withorganic filters. The main characteristics of inorganicfilters are their low skin permeability and their highphotostability, that is, their ability to maintainphotoprotection even after long periods of sunlight. 7 Organic filters are molecules that interfere withincident radiation through the mechanism ofabsorption, when the filter acts as an exogenouschromophore by absorbing a photonof energy andevolving to the excited state of the molecule.

7 Uponreturning to the stable state (unexcited), the release ofenergy occurs at a longer wavelength, either in therange of visible light (as fluorescence) or in the rangeof infrared radiation (as heat). The process can berepeated numerous times by a mechanism calledresonance. Depending on their capacity to absorbshorter or longer wavelengths, organic filters can besubclassified into UVA filters, UVB filters and filters forbroad-spectrum protection (UVA and UVB). 9 The legislation (FDA 99) 10classifiessunscreens as nonprescription medication and listssixteen (16) substances approved as UV filters,allowed for use in Brazil, the National Health SurveillanceAgency (ANVISA) 11defines sunscreens as cosmeticproducts and presents a list of permitted ultravioletfilters, containing thirty-eight (38) active development and use of topicalphotoprotectors have always been related to theprevention of the acute effects of sun radiation,especially sunburn.

8 4It was not until after the 1980s, with studiesdemonstrating the role of UV rays in the developmentof skin cancer, that the sunscreen came to beunderstood not only as an agent against sunburn, butalso as an important element in preventing chronicactinic damage, particularly in relation to thedevelopment of skin cancer. 4 Different studies have shown that thesunscreen has a protective effect against chronicactinic use of sunscreens can reduce thenumber of actinic keratoses. to Green, 14only squamous cellcarcinoma, and not basal cell carcinoma, can beprevented by the regular use of , 15in a recent publication, concluded thatthe daily use of photoprotectors reduces the risk ofsquamous cell carcinoma 16presented a work conducted withrats in which he demonstrated the superiority ofbroad-spectrum sunscreens in comparison to othersFIGURE1:Mechanisms of interaction of sunscreens with sun radiationAdapted source: Schalka 6508 Schalka S, Reis VMSAn Bras Dermatol.

9 2011;86(3) protection factor: meaning and controversies509that are not broad spectrum, in the protection againstDNA damage and in the prevention ofphotocarcinogenesis, delaying tumor use of sunscreens has been reported ascapable of preventing the development of skin cancertriggered by UV by decreasing the formation ofcyclobutane-pyrimidine dimers, as well as preventingother immunological effects induced by UV rays, suchas the suppression of contact hypersensitivity study conducted by Hayag, 17in 1997concluded that the application of a sunscreen withSPF 30 before sun exposure can prevent the decreaseof Langerhans cells in the irradiated site and reduceUV-induced suppression in contact hypersensitivity todinitrochlorobenzene (DNCB).With regard to the use of sunscreens and therisk of developing melanoma, the literature stillshows some and Kupelnick 18published a meta-analysis of eleven studies showing that the use ofphotoprotectors has only a small advantage indecreasing the risk of developing , 19however, in a review of only the mostrecently published articles in which only sunscreenswith a high SPF were used, concluded that that theuse of these products seems to offer a clear protectiveeffect against the risk of 2005 Diffey 20presented a review of thesubject, in which the author concluded that recentimprovements in the effectiveness of modernsunscreens will offer additional protection againstmelanoma.

10 But this result will not be seen in thecoming decades .In view of all this, and also with the perceptionof the deleterious effect of UVA radiation on differentphotodermatoses, on the development of skincancers, and on photoaging andphotoimmunosuppression, new UV filters have beendeveloped, with greater photoprotective capacity inthe UVB band and broader absorption spectrum inUVA and UVB. This leads to a leap in photoprotectiveefficacy, particularly in the Sun protection Factor(SPF) value average SPF value of products used inEurope in 1984 was from four (4) to six (6),progressing to 6 to 10 in 1987 and to about 15 in1997, showing the recent evolution ofphotoprotectors. 20 According to the International Agency forResearch on Cancer (IARC), 21despite insufficientevidence that sunscreens have a protective effectagainst BCC and melanoma, and only limitedevidence that they prevent SCC, the use of thesunscreen should be considered as part of a completephotoprotection better photoprotective efficiency, thesunscreen should present in its compositionultraviolet filters with an absorption spectrum in therange of UVA and UVB rays and be , for an ideal protective effect, the productshould form a homogeneous film, capable ofdelivering its ingredients on a regular basisthroughout the skin surface.