Background: The ultraviolet (UV) erythema test is one of the most frequently used methods to investigate the anti-inflammatory potency of topical dermatological preparations in vivo. Methods: The following questions were addressed in four separate studies with healthy persons (skin types 2 and 3): (1) the optimal localization was determined by comparing light scales on the back, buttocks and volar forearms; (2) the optimal UV-B dose was determined by comparing the 1-fold, 1.5-fold and 2-fold minimal erythema doses (MEDs); (3) hydrocortisone and prednicarbate were evaluated as positive controls, and a sample size calculation was performed, and (4) betamethasone valerate and pimecrolimus were tested as further positive controls in the optimized study model. Results: The back proved to be the best localization for the UV erythema test. It showed a good correlation between the light scale and the test areas. The 1.5-fold MED was the best irradiation dose. In contrast to prednicarbate and betamethasone valerate, hydrocortisone was a rather weak positive control. However, when the sample size was ≧40 subjects, significant results were also obtained with hydrocortisone. Pimecrolimus was not effective in the UV erythema test. Conclusions: The UV erythema test should be performed on the back with at least 40 subjects using the 1.5-fold MED. It may be useful to include a potent corticosteroid, such as prednicarbate or betamethasone valerate, in addition to hydrocortisone. The UV erythema test seems to be suitable only for substances with corticosteroid-like effects, since in this test model the calcineurin inhibitor pimecrolimus was not effective.

Dry skin is associated with a disturbed skin barrier and reduced formation of epidermal proteins and lipids. During recent years, skin-barrier-reinforcing properties of some botanical compounds have been described. Searching the PubMed database revealed 9 botanical extracts that specifically improve skin barrier and/or promote keratinocyte differentiation in vivo after topical application. The topical application of Aloe vera (leaf gel), Betula alba (birch bark extract), Helianthus annuus (sunflower oleodistillate), Hypericum perforatum (St. John’s wort extract), Lithospermum erythrorhizon (root extract), Piptadenia colubrina (angico-branco extract) and Simarouba amara (bitter wood extract) increased skin hydration, reduced the transepidermal water loss, or promoted keratinocyte differentiation in humans in vivo. The topical application of Rubia cordifolia root extract and rose oil obtained from Rosa spp. flowers stimulated keratinocyte differentiation in mouse models. The underlying mechanisms of these effects are discussed. It is concluded that some botanical compounds display skin-barrier-reinforcing properties that may be used in dermocosmetics for dry skin. However, more investigations on the mode of action and more vehicle-controlled studies are required.

After damage to the skin barrier by SLS, pimecrolimus seems to penetrate into the skin as shown by a reduction of the irritation-induced erythma. These data further support the notion that pimecrolimus is selectively effective in the treatment of skin disorders with an impaired function of the epidermal barrier.

St. John's wort (Hypericum perforatum) is a tradional folk remedy that is used for the topical treatment of superficial wounds, scars and burns. A characteristic metabolite of St. John's wort is the photodynamic active plant pigment hypericin. It is known that hypericin may cause a severe photodermatitis called hypericism when higher amounts of St. John's wort are ingested orally. To date, no reports on the photosensitizing capacity of topical application of St. John's wort are available. Here, we investigated the effects of Hypericum oil (hypericin 110 microg/mL) and Hypericum ointment (hypericin 30 microg/mL) on skin sensitivity to solar simulated radiation. Sixteen volunteers of the skin types II and III were tested on their volar forearms with solar simulated radiation for photosensitizing effects of Hypericum oil (n=8) and Hypericum ointment (n=8). The minimal erythema dose (MED) was determined by visual assessment, and skin erythema was evaluated photometrically. With the visual erythema score, no change of the MED could be detected after application of either Hypericum oil or Hypericum ointment (P>0.05). With the more sensitive photometric measurement, an increase of the erythema-index after treatment with the Hypericum oil could be detected (P< or =0.01). The results do not provide evidence for a severe phototoxic potential of Hypericum oil and Hypericum ointment, detectable by the clinically relevant visual erythema score. However, the trend towards increased photosensitivity detected with the more sensitive photometric measurement could become relevant in fair-skinned individuals, in diseased skin or after extended solar irradiation.