Photoaged skin contains elastotic materials in the upper reticular dermis. This phenomenon is commonly known as solar elastosis. In this study, we investigated the effects of heat on the expression of tropoelastin and fibrillin-1, two main components of elastic fibers, and on matrix metalloproteinase (MMP)-12, the most active MMP against elastin, in human skin in vivo. Heat was found to increase tropoelastin mRNA and protein expression in the epidermis and in the dermis. Fibrillin-1 mRNA and protein expression were increased by heat in the epidermis, but were decreased in the dermis. We found that pre-treatment of skin with N-acetyl cysteine or genistein for 24 h prior to heat treatment inhibited the heat-induced expression of tropoelastin, but not of fibrillin-1. These data indicate that reactive oxygen species may play a role in tropoelastin expression by heat, but not in fibrillin-1 expression. We also found that heat treatment increases MMP-12 mRNA and protein expression in human skin. Our results suggest that the abnormal production of tropoelastin and fibrillin by heat in human skin and that their degradation by various MMP, such as MMP-12, may contribute to the accumulation of elastotic material in photoaged skin.