title: Functional properties of the surface of the vermilion border of the lips are distinct from those of the facial skin.
abstract: BACKGROUND
  The vermilion border of the lips (lip for short) is the only part on the face where the oral mucosa is persistently exposed to the outside. Despite its prominent presence on the face, constituting not only the target of cosmetics but also the site for various skin diseases, its functional properties remain almost unknown.
  
  
  OBJECTIVE
  To elucidate the functional properties of the vermilion border of the lips.
  
  
  METHODS
  We studied the biophysical properties of the lip by comparing them with those of the cheek skin in 303 healthy Japanese females aged 21-80 years, in winter. We used a closed-chamber system to measure transepithelial water loss (TEWL) of the lip to avoid the effect of breathing. Moreover, we examined the effects of oral etretinate, a drug that definitely produces dry, scaly lips, on the lips of seven male patients aged 49-89 (average 67) years.
  
  
  RESULTS
  TEWL was significantly almost three times as high on the lips as that on the cheek which is a site that shows far higher levels than do other body areas. TEWL decreased with age more remarkably on the lip than on the cheek. High-frequency conductance, a parameter for surface hydration state, was significantly lower on the lip than on the cheek. The mean values obtained were about one-third of those on the cheek, and no age-related changes were observed either on the lip or on the cheek. The superficial epithelial cells on the lip were parakeratotic and larger than those of the cheek skin. Furthermore, we detected a significant increase in TEWL on the lip as well as on the cheek of patients treated with oral etretinate.
  
  
  CONCLUSIONS
  It appears that the incomplete corneocyte formation of the lip surface is responsible for the poor barrier function and water-holding capacity.
authors.affiliation: Department of Dermatology, Tohoku University School of Medicine, 1-1 Seiryo-machi, Aobaku, Sendai 980-8574, Japan.
authors.forename: H
authors.initials: H
authors.lastname: Kobayashi
authors.forename: H
authors.initials: H
authors.lastname: Tagami
mesh_terms: D000284:Administration, Oral; D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D055592:Biophysical Phenomena; D001703:Biophysics; D002610:Cheek; D004848:Epithelium / Q000502:physiology; D005050:Etretinate / Q000008:administration & dosage; D005260:Female; D005712:Galvanic Skin Response / Q000502:physiology; D006801:Humans; D007641:Keratolytic Agents / Q000008:administration & dosage; D008046:Lip / Q000187:drug effects / Q000502:physiology*; D008297:Male; D008875:Middle Aged; D012879:Skin Physiological Phenomena; D014870:Water Loss, Insensible
chemical_list: D007641:Keratolytic Agents; D005050:Etretinate