First, it may be caused by sweat glands in the anal area, which develop as a result of bacterial infection of the sweat glands in the anal area, and the skin around the anus is darker in color and a hard nodule may appear. Secondly, a hard node in the anus may be caused by folliculitis in the anus, which is caused by a single hair follicle lesion and is difficult to distinguish from sweat gland infection, which may result in anal fistula. When an anal fistula occurs there will be anal swelling and pain with pus and recurrent blood symptoms that require surgery. If there are hard nodes in the anus, it is also necessary to determine whether there are anal papillae or enlargement with anal papilloma, and if there are hard nodes in the anus it may be the presence of rectal submucosal abscess and inflammation of the anal sinus.