Background Questionnaires and lactic acid sting test (LAST) are two widely used methods to identify sensitive skin. However, the self-perceived sensitive skin by questionnaires was not consistent with the determination of LAST. Objective The aim of the study was to measure the biophysical properties noninvasively of sensitive skin evaluated by questionnaire and LAST and to investigate their correlations with the scores of questionnaire and LAST. Methods A total of 209 healthy Chinese females completed the study. Self-assessment questionnaire and LAST were both performed to identify sensitive skin. Epidermal biophysical properties, including skin hydration, transepidermal water loss (TEWL), sebum content, erythema index (EI), a* value, L* value, skin elasticity, and skin pH, were measured with noninvasive instruments. Results The frequency of sensitive skin was 50.2% and 66.0% by questionnaire and LAST, respectively. Subjects with self-assessed sensitive skin had a slightly higher LAST positive rate. Skin hydration, sebum content, a* and EI values were significantly higher in the self-assessed sensitive skin group, while TEWL, a* and EI values increased but L* value decreased with significance in the LAST positive group. The LAST stingers among sensitive skin subjects had higher EI but not in the healthy skin subjects. In addition, questionnaire scores positively correlated with skin hydration, sebum content, a* and EI values, while a positive relationship of LAST scores with TEWL, a* and EI values was observed. The scores of questionnaire and LAST both negatively related to L* value. Conclusion Self-assessed questionnaire is associated with sensitive skin featured by oily and red face without impaired barrier function, whereas LAST is suitable to identify fragile skin barrier and enhanced blood flow on the face. Combination of both methods to diagnose sensitive skin might be more reliable.

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Cosmetic products comprise a variety of nutrient-rich ingredients that favor microbial growth, and the microbial contamination of cosmetics is a health risk for consumers. Preservatives are an essential component to inhibit the development of microorganisms and to prolong the shelf life and usage time of cosmetic products. 1 Unfortunately, preservatives have been reported to cause skin irritation and be a common source of allergies in cosmetic and household products. 2-4 Based on the frequency of use and the prevalence of skin side effects, the prominent preservatives in cosmetics comprise phenoxyethanol, parabens, formaldehyde releasers, isothiazolinones, and organic acids. 5,6 Their health effects are not only due to the induction of skin irritation but also to their multiple sources of exposure resulting in both occupational and nonoccupational contact dermatitis. 7,8 Considering the widespread use of preservatives in daily life, it is a great challenge to evaluate the skin irritation potential of these preservatives and elucidate their underlying mechanisms.

Skin is a natural barrier for the body, and it functions as a connection between the body and the environment. The microecosystem plays an important role in protecting the health of the skin. 1 Probiotics are "live microorganisms, which, when administered in adequate amounts, confer a health benefit to the host." 2 Probiotics supplement nutrition, suppress diarrhoea, prevent intestinal inflammation and exhibit anticolorectal cancer activities. [3][4][5][6] Recent intriguing studies reported that probiotics also exert skin health-promoting effects. Oral probiotics may be effective in treating topical skin conditions, such as psoriasis, acne vulgaris and atopic dermatitis. 7,8 Atopic dermatitis (AD) is a genetically predisposed, recurring allergic skin disease that is characterized by the destruction of the epidermal barrier. 9 Oxidative stress is also one cause of AD 10 . Therefore, strengthening the skin barrier by reducing the level of oxidative stress may reduce the incidence and severity of AD. Notably, topical probiotic formulations to alleviate skin conditions have become a relatively new field of study. Topically applied probiotics in patients with AD reduced skin erythema, scaling and pruritus and improved skin barriers. 11 The Bifidobacteria species is a probiotic and the dominant bacterial species in the human intestinal tract. 12 Oral Bifidobacterium longum (B. longum) preparation effectively reduced the SCORAD