The reasons for the redness of a piece of glans are as follows: 1. The most common is glans vulgaris, because the foreskin is too long and the infection is related to bacteria, fungi, parasites, trichomonas, etc.. When the infection will appear red rash glans, glans foreskin has redness, can be seen vesicular a piece of redness, and finally will be left glans a piece of redness, may have itching pain; 2, drugs or detergent products lead to sequelae symptoms, have had foreskin glansitis after applying drugs, or cleaning glans when using detergent products cause allergies, resulting in foreskin, glans a piece of redness.