title: The skin barrier function: differences between intrinsic and extrinsic aging.
abstract: OBJECTIVE
  Transepidermal water loss (TEWL), stratum corneum hydration (SCH), and the skin surface pH are important parameters to characterize the skin barrier function. The aim of this exploratory study was to compare TEWL, SCH and skin surface-pH on sun-protected versus sun-exposed skin areas in relation to age.
  
  
  METHODS
  Twenty four female subjects with healthy skin were recruited in three age groups. Lifetime sun exposure was assessed using a questionnaire. TEWL, SCH, and skin surface pH were measured on the right upper inner arm, right mid-volar forearm and right dorsal forearm under standardized conditions.
  
  
  RESULTS
  Mean ages (SD) of the three age groups were 33.5 (2.1), 55.4 (2.7), and 76.6 (1.9) years. There were no TEWL differences between the age groups on either skin area. Significantly lower TEWL values were observed on the dorsal forearm compared to the other skin areas (P<0.05). Mean SCH was comparable between the age groups. Higher SCH values were measured on the volar forearm (P<0.05). Skin surface pH on the upper inner arm was significantly higher in the aged group (P=0.023). The dorsal forearm skin had a lower pH than the upper inner arm.
  
  
  CONCLUSIONS
  There seem to be minor changes of TEWL and SCH, but a clear increase of skin surface pH during the course of life. Differences between intrinsically and extrinsically aged skin areas were observed, but results provide no clear evidence for an impairment of the skin barrier function due to photodamage.
authors.affiliation: Clinical Research Center for Hair and Skin Science, Department of Dermatology and Allergy,Charité - Universitätsmedizin Berlin, Berlin, Germany - jan.kottner@charite.de.
authors.forename: C
authors.initials: C
authors.lastname: Trojahn
authors.forename: G
authors.initials: G
authors.lastname: Dobos
authors.forename: U
authors.initials: U
authors.lastname: Blume-Peytavi
authors.forename: J
authors.initials: J
authors.lastname: Kottner
mesh_terms: D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D001132:Arm; D001834:Body Water; D004058:Diffusion; D004781:Environmental Exposure; D004817:Epidermis / Q000737:chemistry / Q000378:metabolism / Q000528:radiation effects; D005260:Female; D005542:Forearm; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008875:Middle Aged; D009928:Organ Specificity; D015595:Skin Aging / Q000502:physiology* / Q000528:radiation effects; D013472:Sunlight; D011795:Surveys and Questionnaires