Skin tests are of paramount importance for the evaluation of drug hypersensitivity reactions. Drug skin tests are often not carried out because of lack of concise information on specific test concentrations. The diagnosis of drug allergy is often based on history alone, which is an unreliable indicator of true hypersensitivity.To promote and standardize reproducible skin testing with safe and nonirritant drug concentrations in the clinical practice, the European Network and European Academy of Allergy and Clinical Immunology (EAACI) Interest Group on Drug Allergy has performed a literature search on skin test drug concentration in MEDLINE and EMBASE, reviewed and evaluated the literature in five languages using the GRADE system for quality of evidence and strength of recommendation. Where the literature is poor, we have taken into consideration the collective experience of the group.We recommend drug concentration for skin testing aiming to achieve a specificity of at least 95%. It has been possible to recommend specific drug concentration for betalactam antibiotics, perioperative drugs, heparins, platinum salts and radiocontrast media. For many other drugs, there is insufficient evidence to recommend appropriate drug concentration. There is urgent need for multicentre studies designed to establish and validate drug skin test concentration using standard protocols. For most drugs, sensitivity of skin testing is higher in immediate hypersensitivity compared to nonimmediate hypersensitivity.

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Regulation of chemokine-mediated leukocyte migration within inflammatory tissues is a complex event that cannot be mimicked and analyzed in vitro.Hapten-induced contact hypersensitivity (CHS) is a highly frequent, often occupationally related human skin disorder in industrialized countries with an enormous sociomedical impact. 1 Moreover, CHS is considered as a standard model for an antigen-specific, T-lymphocytemediated immune response. 2 This concept still holds true for the clinically nonapparent sensitization phase of CHS with antigen-processing and presentation by Langerhans cells and a consecutive T cell stimulation in the draining lymph node. However, there is increasing evidence that during the clinically visible and physically disturbing elicitation phase of CHS nonspecific hapten-induced proinflammatory effects precede or parallel the antigen-specific effect and are a conditio sine qua non for the vigorous inflammatory reactions. 2 In a mouse CHS model Grabbe and colleagues 3 demonstrated that nonspecific effects of epicutaneously applied haptens contribute to the elicitation of CHS. Proinflammatory irritative rather than antigen-specific properties of the hapten are furthermore responsible for the strict concentration-dependence of the effector phase of CHS. Therefore, it is tempting to speculate that such irritative properties of haptens promote inflammatory skin reactions via induction of proinflammatory cytokines, adhesion molecules, and chemoattractants. Accordingly, some contact allergens such as urushiol, the relevant hapten in poison ivy, and nickel sulfate have been demonstrated to directly induce inflammatory activation of keratinocytes resulting in expression of ICAM-1, interleukin (IL)-8, and/or tumor necrosis factor (TNF)-␣. 4 -6 In recent years, in particular chemokines have emerged as potent stimulators of effector cell accumulation and activation and are likely candidates to mediate leukocyte recruitment during elicitation of CHS. Since the description of IL-8 more than a decade ago, the supergene Supported by grants from the W. Sander-Stiftung (95.064.2) (to R. G.) and from the Deutsche Forschungsgemeinschaft (811/1-3) to M. G. M. G. and A. Trautmann contributed equally to this work.

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