The skin is exposed to endogenous and environmental pro-oxidant agents, leading to the harmful generation of reactive oxygen species (ROS). The resulting oxidative stress damages proteins, lipids, and DNA. An imbalance between ROS and antioxidants can lead to an elevated oxidative stress level. Some evidence indicates that allergic and inflammatory skin diseases like atopic dermatitis, urticaria and psoriasis are mediated by oxidative stress. For example, monocytes from patients with atopic dermatitis are primed to generate ROS in response to zymosan, a Toll-like receptor 2 (TLR2) ligand, suggesting that Staphylococcus aureus may damage lesional skin of the disease by production of ROS. Mast cells generate mainly intracellular ROS following the aggregation of FceRI; these ROS may act as secondary messengers in the induction of several biological responses. The present review summarizes the involvement of ROS in the pathogenesis of allergic and inflammatory skin diseases.