title: Menthol concentration in topical cold gel does not have significant effect on skin cooling.
abstract: BACKGROUND
  Topical menthol gels are used in the treatment of various pain conditions. However, the effect of the menthol concentration to skin cooling or cooling sensation is not clear. We hypothesized that increasing menthol concentration enhances skin cooling and causes elevated cooling sensation.
  
  
  METHODS
  Ten healthy male volunteers (age range 25-30 years) were recruited for this study. Application of three gels with different menthol concentrations (0.5%, 4.6% and 10.0%) was tested in random sequence on the left thigh of the subjects. Skin cooling was recorded with a digital infrared camera (FLIR Systems Inc., USA), and cooling sensation was measured with the visual analogue scale rating.
  
  
  RESULTS
  All gels decreased skin temperature significantly (P < 0.05) at least for one hour. However, the variation in menthol concentration seemed not to have a significant effect on skin cooling. Subjects experienced that gel with 4.6% menthol concentration caused significantly stronger cooling effect than 0.5% and 10.0% gels. Gel application had no significant effect on skin temperature in surrounding skin areas.
  
  
  CONCLUSIONS
  In contrast to our hypothesis, menthol concentration was not connected to skin cooling, while moderate menthol concentration of 4.6% may induce stronger cooling sensation compared to low (0.5%) or high (10.0%) concentration gels.
authors.affiliation: Department of Applied Physics, University of Eastern Finland, Kuopio, Finland.|Department of Physical Medicine and Rehabilitation, Kuopio University Hospital, Kuopio, Finland.
authors.forename: R
authors.initials: R
authors.lastname: Lasanen
authors.affiliation: Department of Applied Physics, University of Eastern Finland, Kuopio, Finland.|Department of Clinical Neurophysiology, Kuopio University Hospital, Kuopio, Finland.
authors.forename: P
authors.initials: P
authors.lastname: Julkunen
authors.affiliation: Department of Physical Medicine and Rehabilitation, Kuopio University Hospital, Kuopio, Finland.
authors.forename: O
authors.initials: O
authors.lastname: Airaksinen
authors.affiliation: Department of Applied Physics, University of Eastern Finland, Kuopio, Finland.|Department of Clinical Neurophysiology, Kuopio University Hospital, Kuopio, Finland.
authors.forename: J
authors.initials: J
authors.lastname: Töyräs
mesh_terms: D000287:Administration, Topical; D000328:Adult; D003080:Cold Temperature; D005782:Gels / Q000008:administration & dosage* / Q000737:chemistry*; D006801:Humans; D008297:Male; D008610:Menthol / Q000008:administration & dosage* / Q000032:analysis / Q000737:chemistry*; D012881:Skin Temperature / Q000187:drug effects* / Q000502:physiology*
chemical_list: D005782:Gels; D008610:Menthol
keywords: cold gel; menthol; skin; thermal imaging