The immediate pigment darkening (IPD) response is a transient brownish-gray coloration of the skin of individuals with pigmented skin after irradiation with UVA radiation. The response is evaluated within 60 s after UVA exposure. The IPD protection factor, proposed by Kaidbey and Barnes, is the ratio of the UVA dose required to produce the response, with and without a sunscreen on the skin .
The IPD test produces rapid results with low doses of UVA. However the response is highly variable and difficult to reproduce accurately. Its clinical significance is low because the action spectrum for IPD differs widely from action spectra for erythema and tanning [3,4,21], nonmelanoma skin cancer , and pho-toelastosis . Further, the test is performed using human subjects with skin types III and IV, who are less sun sensitive than types I and II and are not the individuals who have the greatest need for sun protection. (The sun-reactive skin types were characterized by Fitzpatrick .) In addition, the low UVA doses involved may conceal the effects of sunlight on the photostability of the product (see later).
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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.