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Among sensitive skin individuals, there is a subgroup known as stingers, so named because in response to chemical irritants, they experience unusually strong sensations of stinging and burning. Beyond subjective sensory responses to irritants, some stingers also exhibit greater erythematous (objective) responses to irritant exposure.
Early research in 1977 on this subject found that stingers had heightened susceptibility to general irritation.21 However, more recent studies22,23 found no evidence that strong reactivity to one nonimmunological irritant was predictive of such a response to other irritants.22
Studies of skin sensitivity utilizing irritants may be conducted on exposed or partially occluded skin. The characteristics of the vulva differ greatly when compared to exposed skin. In contrast to exposed skin, the vulva is considered occluded tissue, and it also has increased hydration,11 more hair follicles, sweat glands and increased blood flow.10
The current authors recently found that individuals with vulvar erythema at study enrollment also reported significantly more facial erythema resulting from a topical product.24 In many cases, sensitivity in the vulvar region may result from overuse of topical hygienic and medicinal preparations.25 Safety testing of feminine hygiene products considers the potentially higher permeability of vulvar skin and increased secondary sensitization.10
The best method of evaluating vulvar sensitivity to irritation utilizes the combined methods of assessing blood flow, pH and color reflectance.16
Sensitive skin is a subjective, lay term that many consumers claim affects their comfort when using products that contact their skin. Approximately one-half of individuals surveyed in two research studies considered themselves to have sensitive skin.1,2 Researchers know this condition exists, yet it is notoriously difficult to quantify in a meaningful and uniform way. Individuals with sensitive skin typically experience a more rapid and intense sensory response to irritating substances than do people with “normal” skin. In some individuals, this response is reported as stinging (see Stingers) and burning. Moreover, in most cases sensory responses to irritation are not accompanied by erythema or other visible signs of irritation.3
Nonetheless, manufacturers of consumer products such as lotions, soaps, facial tissues, cosmetics and other toiletries continue to seek greater understanding of sensitive skin and sensory responses to irritating substances. In one study, 78% of consumers who considered their skin to be sensitive reported avoiding some products because they experienced unpleasant sensory effects during a previous use.1
Sensitive Skin Responses to Irritants
Research has yielded mixed results about the relationship between subjective sensory response and objective signs of reaction to irritants. A 2005 study evaluated data to determine any correlation between objective scores of erythema and sensory irritation effects reported by participants. The study found a correlation between magnitude of the irritation score (objective) and sensory (subjective) reports of irritation in 13 of 15 participants.4 Another study included participants with sensitive and “normal” skin in the evaluation of facial tissues.5 This study found that the sensory effects were the most reliable indicator of product differences, as opposed to measures of erythema and dryness.
Transepidermal water loss (TEWL) is a biologic endpoint that is an indicator of skin barrier function. Research studies evaluating the association of barrier function and skin sensitivity have shown that a high baseline TEWL was associated with increased sensitivity to a variety of cutaneous irritants using a variety of assessment methods.6
In spite of many inconclusive studies of skin sensory response to irritants, it is known that some individuals have greater sensitivity to irritating substances. Yet, these reactions cannot predict similar reactions to other substances. Sensory reactions to irritants are immediate,7 followed by observable visible signs such as erythema.3
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