What Causes Red Patch On Side Of Penis Head?

i have a red patch on the side of penis head, ibe had it for about a month now, it doesnt cause irritation and dont have any other symptoms, i havent had unprotected sex for 4 years and i been tested which tests came back as negative so im not sure what it is. the doctor i saw said its inlamed he doesnt think its an std but said theyre going to carry out a biopsy. what does this patch sound like to you?