How to tell the difference between chancroid and syphilis?

Genital lesions. Chancroid is a soft friable lesion appearing on mons pubis with surface ulceration. Syphillitic ulcers are more defined, smaller, deeper ulcerated areas which are usually painless (unlike herpetic ulcers). The definitive test is taking swab cultures or biopsies. A blood sample for syphilis (rpr with fta) must be done additionally to confirm before treatment could be started.