Painful Sores on the Penis: Causes and When to Get Evaluated

Why does a genital sore need a clinical eye?

The appearance of a genital sore — its size, base, color, whether it has a crust — overlaps considerably between different conditions 1Ref 1Workowski KA, Bachmann LH, Chan PA, Johnston CM, Muzny CA, Park I, Reno H, Zenilman JM, Bolan GA (2021).Sexually Transmitted Infections Treatment Guidelines, 2021.Differential diagnosis of genital ulcers including herpes, syphilis, and chancroid; clinical evaluation approach and recommended STI testing panel including syphilis serology and HIV testing. Herpes blisters and a syphilis chancre can both appear as an ulcer and look similar without laboratory confirmation. Getting the right diagnosis matters because the treatments are completely different: antiviral medication for herpes, antibiotics for syphilis. Misidentifying one for the other — or reassuring yourself it is nothing — can allow the infection to progress and can lead to unintentional transmission 1Ref 1Workowski KA, Bachmann LH, Chan PA, Johnston CM, Muzny CA, Park I, Reno H, Zenilman JM, Bolan GA (2021).Sexually Transmitted Infections Treatment Guidelines, 2021.Differential diagnosis of genital ulcers including herpes, syphilis, and chancroid; clinical evaluation approach and recommended STI testing panel including syphilis serology and HIV testing.

What are the most common causes of penile sores?

Herpes simplex virus (HSV-1 or HSV-2): The most common infectious cause of painful genital sores. Typically causes clusters of small blisters that break open and leave raw, tender ulcers. A first outbreak may be accompanied by flu-like symptoms. Herpes is not curable but is very manageable with antiviral therapy, which reduces outbreaks and lowers transmission risk 2Ref 2Centers for Disease Control and Prevention (2021).Herpes Simplex Virus — STI Treatment Guidelines 2021 (Web Chapter).HSV as the most common cause of painful genital ulcers; herpes PCR swab as the preferred diagnostic test for active sores; antiviral management.

Syphilis (primary chancre): Causes a firm, round ulcer that is often painless or only mildly tender. It typically appears 10 to 90 days after exposure, and it heals on its own — but the infection progresses if untreated 3Ref 3Centers for Disease Control and Prevention (2021).Syphilis — STI Treatment Guidelines 2021 (Web Chapter).Primary syphilis presentation as a firm painless or mildly tender chancre; incubation period 10–90 days; sore heals spontaneously without resolving the underlying infection. A painless sore is not a reason to dismiss it; it is a reason to get tested.

Balanitis: Inflammation of the head of the penis — sometimes infectious (yeast or bacteria), sometimes from skin irritation. More common in uncircumcised individuals or people with diabetes. Causes redness and soreness rather than a discrete ulcer.

Friction sore or abrasion: From vigorous sex, tight clothing, or masturbation. Typically heals within a few days without other symptoms. A clear mechanical explanation and rapid healing are reassuring, but a sore that persists beyond a week warrants evaluation.

Chancroid: A bacterial STI causing a very painful ulcer with a ragged edge. Less common in many high-income countries but present in some regions and travel-related contexts 1Ref 1Workowski KA, Bachmann LH, Chan PA, Johnston CM, Muzny CA, Park I, Reno H, Zenilman JM, Bolan GA (2021).Sexually Transmitted Infections Treatment Guidelines, 2021.Differential diagnosis of genital ulcers including herpes, syphilis, and chancroid; clinical evaluation approach and recommended STI testing panel including syphilis serology and HIV testing.

What does a clinical evaluation involve?

A clinician will examine the sore, ask about your sexual history, and ask when and how it appeared. They will likely take a swab of the sore for herpes PCR testing — the most sensitive method for active sores 2Ref 2Centers for Disease Control and Prevention (2021).Herpes Simplex Virus — STI Treatment Guidelines 2021 (Web Chapter).HSV as the most common cause of painful genital ulcers; herpes PCR swab as the preferred diagnostic test for active sores; antiviral management — and order blood tests for syphilis, HIV, and other STIs 1Ref 1Workowski KA, Bachmann LH, Chan PA, Johnston CM, Muzny CA, Park I, Reno H, Zenilman JM, Bolan GA (2021).Sexually Transmitted Infections Treatment Guidelines, 2021.Differential diagnosis of genital ulcers including herpes, syphilis, and chancroid; clinical evaluation approach and recommended STI testing panel including syphilis serology and HIV testing. The conversation is clinical, confidential, and non-judgmental; clinicians see these concerns regularly.

If the diagnosis is uncertain after the initial workup, referral to a dermatologist or sexual health specialist may follow.

What to do while waiting for your appointment

• Avoid sexual contact while an active sore is present — this protects potential partners regardless of the cause
• Do not pop blisters or apply OTC creams without guidance; this can alter the sore's appearance and make diagnosis harder
• Keep the area clean and dry
• If significant discomfort is present, a clinician can advise on pain relief once you are seen

Try to remember when the sore first appeared, whether you noticed any tingling or burning beforehand, and any relevant recent sexual history — this information helps a clinician narrow the differential quickly.