Nummular dermatitis is characterized by round or oval-shaped itchy lesions, and is also known as discoid dermatitis. The disorder is recurrent and chronic, and may appear at any age, although it is most common in people in their 60's. The coin-shaped patches can affect any part of the body, but the most common areas are the legs and buttocks. Flare-ups are associated with dry skin, so the winter season is a particularly bad time for those with this condition. It's aetiology remained unknown, and possibly multi-factor. Suspected infection played a role in nummular dermatitis, with the discovery of colonies of Staphylococcus and Micrococcus increased in the abnormality, although clinically not found signs of infection. In this work, the authors reported one case of nummular dermatitis on a 33-years-old woman treated with cold atmospheric argon plasma, showed clinical improvement.