Reactive oxygen species (ROS) are any usually highly reactive chemical compounds that contain an oxygen atom with an unpaired electron in their structure. In physiological conditions, they are involved in many metabolic reactions in the body, while they are also involved in the pathogenesis of diseases such as atopic dermatitis, allergic rhinitis and asthma. Excessive ROS and antioxidant barrier dysfunction cause oxidative stress, resulting in increased oxidative damage in cells, disruption of their proper functioning and induction of a chronic inflammatory process.