A red patch on the arm is considered to have the following disease possibilities: the first condition is dermatophytosis. It can appear as edematous erythema with clearer boundaries and higher skin temperature, on which there can be blisters of corn to bean size. It is mainly caused by a decrease in the immunity of the body and a small local break that leads to hemolytic streptococcal infection. The second condition is sunburn. It is mainly caused by ultraviolet radiation that causes allergic reactions in the arms. The third condition considers common psoriasis. In addition to a red patch, silvery white scales can be seen on top of the erythema, and a typical rash can be seen especially on the elbow extensor side, mainly due to genetic or immune disorders, trauma, pharyngitis, cold and other infectious conditions.