An explanation for the 'placebo' effect of bland ointment bases.

Bland topical applications, containing no pharmacologically active ingredients, were found to have an antimitotic effect on the epidermis of the stripped dorsal skin of hairless mice. White soft paraffin, cetomacrogol cream A (B.P.), starch paste, and emulsifying ointment (B.P.) were applied for 24 h periods under occlusive dressing to the backs of mice. The antimitotic effect was present at the time of removal of the dressings and up to 72 h after removal. White soft paraffin had the maximal antimitotic activity and epidermis of mice treated with it showed only 23% of the number of mitoses of control animals having no such treatment. Emulsifying ointment had the least activity and in some circumstances actually seemed stimulatory to mitotic activity.