title: Methylchloroisothiazolinone and methylisothiazolinone allergic contact dermatitis and the effect of patch test concentration.
abstract: BACKGROUND
  The isothiazolinones methylchloroisothiazolinone and methylisothiazolinone (MCI/MI) are the active ingredients in a frequently used preservative in cosmetic, household, and industrial products.
  
  
  OBJECTIVE
  This study reviewed our department's cases of allergic contact dermatitis caused by MCI/MI, outlining their clinical presentation and possible sources of sensitization. The effect of changing the concentration of MCI/MI from 0.01% to 0.02% in the British Society for Cutaneous Allergy baseline series was also measured.
  
  
  METHODS
  A total of 964 patients were patch tested to the British Society for Cutaneous Allergy baseline series in our department over 4 years. Patients were tested either to 0.01% MCI/MI (697) or 0.02% MCI/MI (267).
  
  
  RESULTS
  Twenty-one patients (2.2%) had positive reactions to MCI/MI. Of patients tested to 0.02% MCI/MI, 3.8% had a positive reaction compared with 1.6% of those tested to MCI/MI 0.01%. Ten patients (48%) had perianal dermatitis; of these, 50% had used moist toilet wipes.
  
  
  CONCLUSIONS
  We highlight MCI/MI as important contact allergens found in moist toilet wipes and should be considered particularly in patients with facial, hand, and perianal allergic contact dermatitis. Patch testing to 0.01% MCI/MI may underestimate its allergenic potential, missing more than half of allergic cases compared with testing to 0.02%. To identify isothiazolinone allergy, we recommend that 0.02% MCI/MI should be used in baseline series.
authors.affiliation: Department of Dermatology, St. Vincent's University Hospital, Dublin, Ireland. higgins_eleanor@hotmail.com
authors.forename: Eleanor
authors.initials: E
authors.lastname: Higgins
authors.forename: Brian
authors.initials: B
authors.lastname: Kirby
authors.forename: Sarah
authors.initials: S
authors.lastname: Rogers
authors.forename: Paul
authors.initials: P
authors.lastname: Collins
mesh_terms: D017449:Dermatitis, Allergic Contact / Q000209:etiology*; D004202:Disinfectants / Q000009:adverse effects*; D005260:Female; D006795:Household Products / Q000009:adverse effects; D006801:Humans; D008297:Male; D010328:Patch Tests / Q000379:methods*; D011310:Preservatives, Pharmaceutical / Q000009:adverse effects*; D012189:Retrospective Studies; D013844:Thiazoles / Q000009:adverse effects*
chemical_list: D004202:Disinfectants; D011310:Preservatives, Pharmaceutical; D013844:Thiazoles; C011506:2-methyl-4-isothiazolin-3-one; C011421:5-chloro-2-methyl-4-isothiazolin-3-one