Genital herpes simplex is the most common cause of genital ulcers in the world. Primary syphilis and chancroid may have a similar appearance. Molluscum contagiosum can sometimes become inflamed and look like a herpetic lesion. There are many other diseases that cause inflammation and erosions but these can usually be easily differentiated from herpes simplex by physical examination.

A case of primary syphilis showing three genital ulcers. These ulcers are typically painless.

Molluscum contagiosum is a contagious viral infection. The lesions consist of firm white papuals.