INTRODUCTION
The effectiveness of topical acne therapy is related to
adherence with the regimen by the patient, which is
influenced directly by the ability to apply anti-acne
preparations appropriately. Although truncal acne is less well
studied than facial acne, there has been increasing attention on
its evaluation and management.1,2
Most patients with truncal acne present with concurrent facial
acne: a study of truncal acne demonstrated that 48 percent
of patients had acne solely on the face while 52 percent also
had truncal acne.1 Only two percent of patients had solely
truncal acne. In a more recent study of patients referred by
primary care physicians to dermatologists for the treatment
of acne, the prevalence of facial acne was 93 percent while
the prevalence of chest and back acne was 45 and 61 percent,
respectively.3
Topical treatment of truncal acne presenting on the chest, back
and shoulders can be challenging as it requires application
of anti-acne preparations to a difficult to reach, broad surface
area. In addition, there is no effective treatment for truncal acne
scarring once it develops, so effective acne therapy is important
to prevent lesion development and scar formation.4
Due to the extensive surface area of the back, it is important
that the appropriate vehicle be selected that can be conveniently
and efficiently applied. Formulations that exhibit ease of
spreadability and lack of residue, such as cleansers and foams,
may be more applicable for truncal application.5,6
Benzoyl peroxide (BP) is extensively utilized as a topical agent
for the treatment of acne.7 BP alone or in combination with
clindamycin reduces Propionibacterium acnes (P. acnes) and
reduces the emergence or proliferation of antibiotic-resistant P. acnes strains.7–9 Importantly, P. acnes organisms resistant to
BP have not been identified nor would it be expected since this
agent is a non-antibiotic antimicrobial.7
BP exerts its therapeutic effect in acne through reduction of P. acnes as demonstrated by a 1.0–2.0 logarithmic colony reduction
on the face. “Leave-on” BP formulations have been shown
to provide greater reduction in P. acnes than “wash-off” formulations.10,11 BP “wash-off” formulations have been shown to be
effective in reducing P. acnes populations on the face.12,13 Interestingly,
the author could find no published data on P. acnes reduction on the back for any BP formulation.
“Wash-off” formulations of BP are frequently recommended
for the treatment of truncal acne due to patient convenience
of application in the shower as well as to minimize bleaching
potential.14,15
The purpose of this study was to evaluate the in vivo effects
on P. acnes levels on the back with use of a BP (5.3%) emollient
foam and a BP (8%) wash by quantitative microbiologi-
