Quantification of natural moisturizing factors at the skin surface using a portable infrared spectrometer device: a pilot, calibration model

Attenuated total reflectance Fourier transform infrared spectroscopy (FTIR) is a useful technique for the molecular analysis of surfaces, including the skin, with promising translational clinical potential. Skin‐surface levels of natural moisturizing factor (NMF) are a biomarker of filaggrin (FLG) status (both inherited and acquired) and skin dryness. FLG‐related atopic dermatitis (AD) is associated with more severe and persistent disease. The objective of this study was to combine FTIR with chemometric analysis to generate a pilot calibration model for the in vivo quantification of NMF at the skin surface using a portable FTIR device. This study was performed in a climate‐controlled, skin barrier suite located at the University of Sheffield, U.K. patients with either healthy skin or AD were recruited from the local Sheffield community, and informed consent was obtained prior to enrolment in the study. A diagnosis of AD was made using the U.K. working party criteria, and disease severity was classified by the Eczema Area and Severity Index score. Genotyping for the five most common European loss‐of‐function FLG mutations was performed from buccal swabs. FTIR spectra of 4‐cm−1 resolution were collected from the volar forearm and antecubital fossa in conjunction with tape strips for the quantification of NMF components by high‐performance liquid chromatography (HPLC) and o‐phthaldialdehyde derivatization. Transepidermal water loss (TEWL) and stratum corneum hydration (SCH) measurements were collected as an assessment of barrier function. Ethical permission for this study was granted by the National Health Service Trent research ethics committee. Partial least‐squares regression modelling of absorbance in the mid infrared spectral region (1710–1185 cm−1) with skin‐surface NMF components determined by HPLC generated a predictive r2 value of 0.90. Modelling was superior on the antecubital fossa compared with the forearm, presumably due to the increased FTIR signal obtained from this site. Predicted NMF values correlated with FLG status, TEWL and SCH. FTIR combined with chemometric analysis is a suitable technique for the instantaneous in vivo quantification of NMF at the skin surface. The use of a portable FTIR device makes this methodology suitable for any clinical setting, with the potential to inform long‐term treatment strategies in AD