A major disadvantage of all in vivo methods is that available UV sources, when filtered to remove the UVB portion of the spectrum, do not fully reproduce the UVA portion of the solar spectrum .
Sunscreen UVA protection may be evaluated by measuring the product UV transmission spectrum determined in vitro. Once a valid transmission spectrum has been measured for a given product, the degree of UV protection against any effect for which an action spectrum is known may be assessed for any known natural or artificial UV source. The product UV transmission spectrum may be validated by computing the SPF and comparing the SPF determined in vitro to that measured in human subjects. If the SPF calculated from in vitro measurements matches that measured in human subjects, then the UVA protection factor (PFA), or the ratio of UVA protection to overall protection may be computed for any solar spectrum considered relevant to the human exposure situation in question.
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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.