Citric acid is an alpha-hydroxyacid (AHA) widely
used in cosmetic dermatology and skincare products. However,
there is concern regarding its safety for the skin. In this study,
we investigated the cytotoxic effects of citric acid on the
human keratinocyte cell line HaCaT. HaCaT cells were treated
with citric acid at 2.5-12.5 mM for different time periods. Cellcycle
arrest and apoptosis were investigated by 4,6-diamidino-
2-phenylindole dihydrochloride (DAPI) staining, flow
cytometry, western blot and confocal microscopy. Citric acid
not only inhibited proliferation of HaCaT cells in a dosedependent
manner, but also induced apoptosis and cell cyclearrest
at the G2/M phase (before 24 h) and S phase (after 24
h). Citric acid increased the level of Bcl-2-associated X
protein (BAX) and reduced the levels of B-cell lymphoma-2
(BCL-2), B-cell lymphoma-extra large (BCL-XL) and activated
caspase-9 and caspase-3, which subsequently induced
apoptosis via caspase-dependent and caspase-independent
pathways. Citric acid also activated death receptors and