In this study, we investigated cellular damages by acute and chronic infrared-A rays using a customized solar infrared-A simulator (infrared-A intensity of 42 mW/cm2) at well-controlled temperature conditions. At physiological temperature (34°C), acute infrared-A irradiation on fibroblasts showed negligible effects on cell proliferation while there was slight changes in several gene expression e.g. matrix metalloproteinase-1 and collagen type-1 α-1 genes. Acute infrared-A irradiation only with heat stress (43°C) elicited reduced cell proliferation and decrease of procollagen type 1 C-terminal peptide. On the other hand, repeated infrared-A irradiation for 24 days (chronic infrared-A irradiation) significantly reduced cell proliferation, increased cellular reactive oxygen species, and elicited cellular apoptosis and morphological changes at physiological temperature. In particular, the degree of cellular responses by infrared-A was dependent on types of fibroblasts from different donors. In addition, the harmful effects by infrared-A irradiation on human fibroblasts were greatly protected with titanium dioxide-based emulsion. Taken together, it is crucial to protect skin from harmful damages by chronic infrared-A for healthy skin and well aging during daily life.