Characterization and validation of an in vivo confocal Raman spectroscopy led tri-method approach in the evaluation of the lip barrier

Human lip vermilion: Physiology and age-related changes

BACKGROUND

The human lip vermilion, also known as the red lip, is important to the quality of life and has long attracted the attention of cosmetic researchers. However, there is limited existing literature on the physiological characteristics and age-related alterations in the human vermilion.

OBJECTIVE

We aim to provide an overview of the physiological characteristics and age-related alterations in the human vermilion.

METHODS

This article is a result of previous research. We conducted a literature search using various academic databases such as Google Scholar, Web of Science, and PubMed. Our findings provided a comprehensive understanding of the physiological characteristics and age-related changes of the human lip vermilion.

RESULTS

The human lip vermilion has a unique structure and physiological characteristics, and during the aging process, a few changes may occur in the human lip vermilion.

CONCLUSION

Understanding the human lip vermilion's physiological characteristics and age-related changes can provide key information for the future innovation of lip vermilion care products. Further investigations are necessary to reach a consensus on the physiological characteristics and age-related alterations in the human vermilion.

Stratum corneum hydration in healthy adult humans according to the skin area, age and sex: a systematic review and meta-analysis

Stratum corneum (SC) hydration is one of the most important skin biophysical parameters, which is affected by age, sex and anatomic site. We conducted a systematic review and meta-analysis to provide detailed information on baseline values of SC hydration in healthy human adults, according to the skin area, age and sex. The databases Medline, Embase, Web of Science and Scopus were searched for primary reports, with in vivo corneometry measurements, which were conducted on disease-free skin of human subjects, aged 18+ years in English. Risk of bias was evaluated using the critical appraisal tools for JBI Systematic Reviews, and only low-risk studies were selected. The comparison was performed in each skin area between males and females and also between young- and middle-age subjects. Among 323 Retrieved titles, full texts of 259 articles were read, and 240 studies were excluded due to unclear or insufficient reporting of SC hydration, as well as high or medium risk of bias. 19 studies (including 113 records) providing data about SC hydration in 12 skin areas were included in the final data synthesis. Pooled sample sizes ranged from n = 32 for lips to a maximum of n = 3202 for cheeks. The lowest hydration of 12.5 [95% CI 11.05-13.94] was reported for the back, and the highest hydration of 64.34) [95 CI% 62.07-64.59] for the periorbital area. Facial skin showed higher water content compared with other areas. There were also site-dependent differences in the hydration level of the facial skin. Comparisons between two age groups, and male and female participants, did not show any statistically significant differences. The main limitation was we included studies using only one measurement device. The quality of reporting SC hydration in humans should be increased in future studies.

Higher Accumulation of Docosahexaenoic Acid in the Vermilion of the Human Lip than in the Skin

The vermilion of the human lip is a unique facial area because of certain distinguishing features from the adjacent tissues such as the white lip (skin) and oral mucosa. However, the distinction in terms of molecular distribution between the vermilion and skin has remained unexplored. Therefore, we aimed to map the human lip by mass spectrometry imaging to gain understanding of the free fatty acid distribution in the vermilion. The lip specimens trimmed off during cheiloplasty were analyzed using desorption electrospray ionization-mass spectrometry imaging. Distributions of two monounsaturated fatty acids and three polyunsaturated fatty acids were observed in the human lip tissue: palmitoleic acid (POA) and oleic acid (OA) and linoleic acid (LA), arachidonic acid (AA), and docosahexaenoic acid (DHA), respectively. Although POA, OA, LA, and AA were differentially distributed across the vermilion and skin, DHA showed a higher accumulation in the epithelium of the vermilion compared to that in the skin. Our results clearly demonstrated the difference in fatty acid distributions between the vermilion and skin. The highly abundant DHA in the epithelium of the vermilion may have an antioxidant role and may thus protect the lip from aging. Our findings can provide a novel strategy for treating lip disorders.

Characterization and validation of an in vivo confocal Raman spectroscopy led tri-method approach in the evaluation of the lip barrier

Background/Aim

It was the aim to establish and validate in vivo confocal Raman spectroscopy for characterization of the lip barrier in conjunction with transepidermal water loss (TEWL) and skin capacitance assessments. For the first time in vivo, barrier‐relevant components of the lip (derived, natural moisturizing factors (NMFs) and ceramides are described.

Methods

In 32 healthy volunteers, a dental tongue fixation device was inserted to prevent both voluntary and involuntary lip moisturization during measurements. Seventeen individual parameters relating to water, ceramide, and NMF content were assessed via Raman spectroscopy. Additionally, corneometry and TEWL were measured. To give a guidance for the required volunteer group size of future lip barrier studies for all test parameters, coefficients of variation (CV) were calculated and plots showing the required sample size for a given percentage treatment effect.

Results

Raman spectroscopy assessed parameters on the lower lip comprehensively characterized the state of the lip barrier. Parameter variability was sufficiently low to corroborate changes in most parameters using relatively small study populations.

Conclusions

Lip skin is comparatively well hydrated. Biophysical measurement of the lip barrier function is a challenge, as unconscious licking of the lower lip has to be prevented. In vivo confocal Raman spectroscopy provides insightful parameters for the characterization of the lip barrier and sufficiently low inter‐individual variability to assess relatively small parameter changes employing relatively few study subjects. Differences at the molecular level and at a high spatial resolution are detectable, and these insights might provide a breakthrough in the evaluation of lip barrier function and developing solutions for lip care.