title: A fundamental investigation into aspects of the physiology and biochemistry of the stratum corneum in subjects with sensitive skin.
abstract: BACKGROUND
  Sensitive skin is a poorly understood skin condition. Defects in stratum corneum (SC) barrier function and/or extrasensory neuronal networks in the epidermis are believed to be involved in the problem.
  
  
  OBJECTIVE
  This study aimed to unravel the relationships between bleomycin hydrolase (BH) and calpain-1 (C-1), pyrrolidone carboxylic acid (PCA) levels, corneocyte maturation, transglutaminase (TG) and plasmin activities on the cheeks of subjects with sensitive skin.
  
  
  METHODS
  Forty-eight female Caucasian subjects, Fitzpatrick skin phototypes II-III, with self-perceived sensitive facial skin, were assessed and underwent a capsaicin reactivity test. Expert grading of skin condition was conducted as well as the measurement of transepidermal water loss (TEWL), skin capacitance, SC cohesion and SC integrity. BH, C-1 and plasmin activities were measured as well as PCA levels, plasmin and TG activity. Differential Nile red and involucrin immunostaining was performed to assess corneocyte maturation and size.
  
  
  RESULTS
  About 52% of the subjects reacted to capsaicin. There were no significant differences between the capsaicin-sensitive and non-capsaicin-sensitive subjects with reference to skin grading, TEWL, skin capacitance and SC cohesion. PCA levels and BH activity were lowest in the capsaicin-sensitive panel (P < 0.05) and were correlated in non-capsaicin-sensitive subjects (r = 0.72). The activity of TG was significantly lower (48%) in the capsaicin-sensitive subjects (P < 0.001) and their corneocytes were less mature and smaller (P ≤ 0.05). SC was estimated to be thinner (6.87 ± 0.28 vs. 8.68 ± 0.26 μm; P = 0.001) in the capsaicin-sensitive subjects with a corresponding shorter SC path length (83.2 ± 4.4 μm and 113.1 ± 4.5 μm; P = 0.001).
  
  
  CONCLUSIONS
  Despite the physiological similarities between the two groups of sensitive skin subjects, differences in their biochemistry were clearly evident. Lower levels of PCA, BH and TG activities together with a greater number of smaller and immature corneocytes indicate inferior SC maturation in the capsaicin-sensitive subjects. The reduced maturation of corneocytes and thinner SC likely contributes to a greater penetration of capsaicin and the associated increased skin sensitivity.
authors.affiliation: UCL School of Pharmacy, London, UK.
authors.forename: N
authors.initials: N
authors.lastname: Raj
authors.affiliation: DSM Nutritional Products Ltd., Kaiseraugst, Switzerland.
authors.forename: R
authors.initials: R
authors.lastname: Voegeli
authors.affiliation: UCL School of Pharmacy, London, UK.
authors.forename: A V
authors.initials: AV
authors.lastname: Rawlings
authors.affiliation: DSM Nutritional Products Ltd., Kaiseraugst, Switzerland.
authors.forename: S
authors.initials: S
authors.lastname: Doppler
authors.affiliation: DSM Nutritional Products Ltd., Kaiseraugst, Switzerland.
authors.forename: D
authors.initials: D
authors.lastname: Imfeld
authors.affiliation: UCL School of Pharmacy, London, UK.
authors.forename: M R
authors.initials: MR
authors.lastname: Munday
authors.affiliation: UCL School of Pharmacy, London, UK.
authors.forename: M E
authors.initials: ME
authors.lastname: Lane
mesh_terms: D000328:Adult; D002211:Capsaicin / Q000008:administration & dosage; D005260:Female; D006801:Humans; D008875:Middle Aged; D011761:Pyrrolidonecarboxylic Acid / Q000378:metabolism; D012684:Sensory Thresholds; D012879:Skin Physiological Phenomena
chemical_list: D002211:Capsaicin; D011761:Pyrrolidonecarboxylic Acid
keywords: biomarkers; protease activity; sensitive skin/inflammation/allergy; skin physiology/structure