On the evening of October 12, it was found that there were some redness and swelling on the inner side of the left arm joint, and there would be pain when pressing. Ulceration occurs on October 13, and slight touch will cause obvious pain
According to your picture above, there are some redness and swelling in the joint. In this case, it may be due to excessive sweating or excessive friction. This can lead to injury or dermatitis. It is recommended to apply erythromycin ointment or baiduobang ointment. Sweat less and exercise less recently. If you don't get better, go to the hospital for face-to-face diagnosis.
According to the situation you described, some redness and swelling on the inner side of the left arm joint have pain and tenderness. According to the picture, it may be the symptoms of local infection caused by local contusion. Therefore, it is necessary to protect the wound and apply some antibiotic ointment locally, such as erythromycin, baidobang, etc., to effectively control the disease. Generally, scab can be healed after two weeks.
This consideration is also a contact dermatitis. I don't know what stimulates the inflammation of this skin. In this case, it is recommended to disinfect with Iodophor every day, rinse with normal saline, and then apply some growth factors, such as beifuxin.