[Contact eczema induced by propylene glycol. Concentration and vehicle adapted for for patch tests].

INTRODUCTION

Contact dermatitis to propylene glycol, a widely used compound, is often difficult to evidence with skin tests.

CASE REPORTS

We observed three cases of contact eczema to a dermal cream (Zovirax) used for labial herpes simplex. Patch-tests were positive in all three cases when the entire product was used but negative for each of the constituent components. The initial diagnosis could be an allergic reaction to the composition between the components as has been described elsewhere. Skin tests were completed with patch-tests using propylene glycol at concentrations over 5 p. 100 or with a vehicle other than vaseline (commercial tests use 5 p. 100 propylene glycol in vaseline). The results of these tests provided evidence allowing the diagnosis of contact dermatitis to the dermal cream due to allergic reaction to propylene glycol.

DISCUSSION

Our three cases illustrate the frequency of false negative reactions to propylene glycol on commercial patch-tests. In agreement with data in the literature, these tests show that propylene glycol must be used at concentrations up to 10 to 20 p. 100 to identify allergic reactions with patch-tests.