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The biological activity and efficacy of a suncare product, as represented by the SPF, is evaluated by its ability to protect human skin from erythema and edema. It is measured by determination of the dose which is required to induce a just perceptible redness (MED = minimal erythema dose) on untreated and on sunscreen-treated skin. The SPF is defined as the ratio of the dose of UV radiation required to produce a minimal erythematic response 24 h after exposure on protected skin after application of 2 mg/cm2 of a sunscreen product to the dose needed to produce the same degree of erythema in unprotected skin (SPF = MED of sunscreen-treated skin/MED of unprotected skin). The SPF is therefore a useful assessment of primarily UVB (290-320 nm) filters. However, the SPF test does not adequately assess the complete photoprotective profile of sunscreens, specifically against long-wavelength UVA1 (340-400 nm).

Currently, the SPF scale specified in a sunscreen product applies solely to UVB protection [5]. Because UVA is far less erythematogenic (by a factor of 1,000) than UVB, using erythema as the endpoint of testing becomes problematic, as the length of time required for volunteers to remain immobile during testing is too long to be practical.

For labeling UVA, there exists no worldwide consensus [9]. Protocols have used immediate pigment darkening, delayed tanning and erythema with and without photosensitizer as in vivo methods. An in vitro method measures the absorption of UV radiation by sunscreen material and establishes the critical wavelength, the wavelength below which 90% of a sunscreen's UV absorbance occurs [8].

It has been found that patients or consumers normally apply much lower amounts of sunscreens than the amounts of 2 mg/cm2 used under laboratory conditions for determining the SPF rating of a specific sunscreen product. Debuys et al. [10] reported that consumers normally applied between 0.5 and 1 mg/cm2 of the sunscreen product, therefore when patients use an SPF 30+ sunscreen in real life, the UVB protection might be much lower than the indicated one. Additionally, as commercial SPF testing is only conducted on subjects of Fitzpatrick's skin types I—III (table 1), and preferentially on those with skin types I and II, this could be an important cause of laboratory overestimation of sunscreen efficacy during outdoor activities in a genetically diverse population of sunscreen users. Therefore, factors such as the differences in skin color and MED between the subjects used for SPF testing and the general population, the spectral differences between sunlight and artificial UV as well as the tendency of the public to apply only small amounts of sunscreen and to reapply it infrequently, mean that laboratory and sunlight SPFs may be markedly different. In conclusion, multiple factors, such as UV source, sunscreen application, skin color and erythemal susceptibility in volunteers, interact to produce substantially lower SPFs in natural sunlight than in the laboratory, and differing SPFs between laboratories [11].

However, apart from erythema, sunlight triggers many biological processes such as photoaging, immune suppression and mutation of skin cells. Therefore, it has recently been suggested that the SPF value may not be a sufficient gauge of the sunscreen's ability to protect against the many harmful biological reactions induced by sunlight. For instance, UV-induced immune suppression can be caused by radiation below the erythemal dose [4]. Based on these reflections, an immune protection factor as a measure of the effectiveness of a sunscreen

Table 1. Human skin types and their reactivity to sunlight (modified according to Fitzpatrick)

Skin phototype

Skin color without exposure to sun

Sensitivity to UV radiation

Tanning history

I

White

Very sensitive

Always burns easily, shows no immediate pigment darkening reaction, never tans

II

White

Very sensitive

Always burns easily, trace immediate pigment darkening reaction, tans minimally and with difficulty

III

White

Sensitive

Burns minimally, immediate pigmentation darkening + , tans gradually and uniformly (light brown)

IV

Light brown

Moderately sensitive

Burns minimally, immediate pigment darkening ++

V

Brown

Minimally sensitive

Rarely burns, immediate pigment darkening +++ , tans profusely (dark brown)

VI

Dark brown

Insensitive or least sensitive

Never burns, immediate pigment darkening reaction + + +, deeply black, tans profusely

product to protect against UV-induced immune suppression and a mutation protection factor as an estimate of a sunscreen's protective activity, as obtained by the measurement of p53 mutation in the skin of mice, were proposed [1].

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How To Deal With Rosacea and Eczema

How To Deal With Rosacea and Eczema

Rosacea and Eczema are two skin conditions that are fairly commonly found throughout the world. Each of them is characterized by different features, and can be both discomfiting as well as result in undesirable appearance features. In a nutshell, theyre problems that many would want to deal with.

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