There are many cosmetic ingredients, such as preservatives and fragrances, known to elicit adverse effects. The aim of this study was to investigate the side-effects of cosmetic preservatives, by evaluating objective and subjective skin irritation. The method comprised of 2 parts. In part 1, we tried to compare 24-hr patch test results with the sensory irritation potential of several preservatives. In part 2, skin cumulative irritation test for 21 days and sensory irritation test were performed to compare various combinations of preservatives in 4 types of formulations. Our data showed that methylparaben, ethylparaben, propylparaben, butylparaben, phenoxyethanol (PE) and chlorphenesin (CPN) have similar objective skin irritation potential at the minimal inhibitory concentration of each preservative, but CPN has higher potential than other preservatives in subjective irritation. Sensory irritation of preservatives changed according to formulation type, and PE combined with CPN highly increased irritation. There was correlation between antimicrobial activity and skin objective irritation but not sensory irritation. Influence on skin sensory irritation varies with the combination of preservatives. Therefore, for the development of new preservatives and cosmetics, it is important to evaluate skin sensory irritation of preservatives used in cosmetic products according to the type of formulations.

Subjective phototype self-assessment showed similar results in Korean and Cantonese. However, objective skin color parameters differed between the two populations. Koreans, who live at a higher latitude and get relatively little sun exposure, have lighter skin color than the Cantonese and burn easily upon UV exposure.

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Background Facial skin redness can have a negative impact on the quality of life. In this study, we investigated the skin biophysical parameters associated with facial skin redness as a function of aging. Methods Our aims were as follows: (1) to understand the impact of non‐pathological facial skin redness on the quality of life of Korean women through a survey; and (2) compare skin biophysical properties between women with and without facial skin redness. Results Women aged between 20 and 39 years perceived their own facial skin redness at a higher rate than those aged ≥40 years. In addition, in redness‐prone women, the intensity of skin redness and skin surface perfusion were higher, while skin hydration was lower regardless of age. In redness‐prone women aged ≥40 years, the values for transepidermal water loss, elasticity, and skin thickness were lower, and the mean pore depth was greater. Facial redness intensity was higher, and the distribution was wider in redness‐prone younger women, while only redness intensity increased in the older age group. Conclusions Overall, redness‐prone women aged ≥40 years had weaker skin properties. Our study indicated the age‐related biophysical characteristics of non‐pathological facial skin redness. We believe that our findings will help improve its negative effects.