INTRODUCTION
Despite its ubiquity, a single definition for “sensitive skin†remains elusive and there is little agreement among dermatologists beyond heightened sensitivity on its symptomatology.1 Most of the research data currently available is based on subjects’ declarations and collected through epidemiological studies.2 Although some 45% of US adults self-report having “sensitive skinâ€, this designation has not been rigorously defined and dermatologists seem largely involved in the care of this condition.2
The literature does support that sensitive skin is frequently associated with adverse reactions to cosmetic products and certain demographic and ethnic populations may have higher rates of sensitive skin.3-5 Sensitive skin has also been associated with an underlying skin disease such as rosacea, or irritant contact dermatitis.4 Some studies have suggested that sensitive skin is associated with impaired barrier function resulting in marked cutaneous responses to otherwise harmless stimuli.1 The scientific community has yet to identify an acceptable screening test for sensitive skin, however, patch testing of patient skincare products is often recommended if no clear pathology is evident. In two studies that patch-tested skincare ingredients, most subjects had at least one reaction indicating a high prevalence of sensitivity to skincare ingredients among some populations.6,7
A number of products are available that are targeted to those with sensitive skin and frequently labeled “hypoallergenicâ€. Labeling a product as hypoallergenic implies it is less likely to cause an allergic reaction, but may also suggest it is gentler or safer for skin. However, there is no federal regulatory definition that governs the term hypoallergenic, rendering the classification as vague.8 Patch-testing studies that evaluate individual ingredients may not be representative of the irritation potential of skincare products as the concentrations tested may be different from those used in the formulated product. Furthermore, vehicles and formulations can affect the sensitivity to a particular ingredient.9 Testing actual skincare products may provide more realistic expectations about the potential for skin reactions and help support claims of hypoallergenicity.
Several methods are used to evaluate the irritation potential of skincare products (Table 1).1 Patch testing is a common and efficient method to assess irritation. A single application of a raw ingredient or a product is applied to skin under an occlusive patch for a designated time period. At the end of the period, the patch is removed and the skin assessed for signs of irritation. However, far more rigorous testing methodologies exist, capable of eliciting more subtle irritant responses and reactions in the setting of damaged skin that might not otherwise be found. Cumulative irritancy testing is similar to patch testing, except patches are applied daily for 23 hours to the same site for 10 days to 21 days and assessed for irritation.1,10 The chamber scarification test involves scratching the volar forearm down to the papillary dermis, applying test material under a chamber system for 3 days, and evaluating the skin for reactions up to 1 week after chamber removal.1 Repeat insult patch testing (RIPT) is a comprehensive form of testing that assesses the potential for both irritation and sensitization.1,9 Patches are applied at the same site every 48 hours to 72 hours, 3 times a week, for 3 weeks to 4 weeks. After a 2-week period with no applications, test materials are
