The placebo response to white soft paraffin/propylene glycol in the skin blanching test

SUMMARY Eight grades of white soft paraffin BP were investigated for their ability to produce pallor of normal skin in a test designed originally for topical corticosteroid activity. All samples produced definite but transient blanching, the extent of which was determined by the grade of white soft paraffin and the test method employed. Pallor was often more pronounced under non‐occlusive test conditions and when the sample contained 5% w/w propylene glycol. Blanching may have been due to the presence of a pallor‐inducing substance transported into the skin by propylene glycol, rather than to a simple hydration effect.