The presence of a new, painful, or unfamiliar sore, blister, or bump in the genital area often leads people to fear a diagnosis of herpes simplex virus (HSV). However, a wide spectrum of conditions, both infectious and non-infectious, can produce lesions that closely mimic a herpes outbreak. Self-diagnosis based on visual symptoms is unreliable and can lead to incorrect management or delayed treatment. Professional medical evaluation is always necessary to accurately identify the underlying cause.
Other Sexually Transmitted Infections That Cause Sores
Several other sexually transmitted infections (STIs) are characterized by sores or ulcers, each with distinct features that differentiate them from the clustered, painful vesicles of a herpes outbreak. Primary syphilis, caused by the bacterium Treponema pallidum, manifests as a chancre. This is typically a single, firm, round ulcer that is notably painless, contrasting sharply with the tenderness and burning associated with herpes lesions. The chancre will often heal without treatment, though the infection itself remains.
Chancroid, a bacterial infection caused by Haemophilus ducreyi, produces ulcers that are the opposite of syphilitic chancres. They are characteristically soft, ragged-edged, and often extremely painful. These ulcers may also be accompanied by tender, swollen lymph nodes in the groin that can rupture and drain pus, a progression less typical of HSV.
Lymphogranuloma Venereum (LGV), caused by specific strains of the Chlamydia trachomatis bacterium, begins with a small, often painless papule or blister that can be overlooked. The most significant symptoms of LGV appear later as severely swollen, tender lymph nodes in the groin.
Localized Infections Not Spread Sexually
Lesions that resemble herpes can also arise from common infections localized to the genital or oral area that are not primarily classified as STIs. Folliculitis, an inflammation of the hair follicles often caused by the Staphylococcus aureus bacterium, presents as small, red bumps or pus-filled whiteheads centered around a hair. This condition is frequently triggered by shaving, friction from tight clothing, or ingrown hairs, and its appearance is more akin to a cluster of pimples than the fluid-filled blisters of HSV.
Molluscum Contagiosum, a viral skin infection caused by a poxvirus, produces small, firm, dome-shaped papules that are typically flesh-colored or white. A distinguishing feature is a small indentation or “dimple” at the center, known as umbilication. While molluscum can be spread through sexual contact, it is also common in children and spreads through non-sexual skin-to-skin contact or shared objects.
A severe, localized yeast infection, or candidiasis, can cause intense redness, inflammation, and deep cracks or fissures in the delicate skin of the vulva or penis. These painful cracks can mimic an open sore, but they are typically accompanied by the thick, white, “cottage cheese-like” discharge characteristic of a fungal overgrowth.
Non-Infectious Dermatological Conditions
Some common mimics of herpes are non-infectious skin conditions resulting from trauma, chemical exposure, or chronic immune dysfunction. Contact dermatitis is a localized inflammatory reaction that occurs when the skin is exposed to an irritant or an allergen. In the genital area, this often results from sensitivity to components in laundry detergents, scented soaps, lubricants, or latex condoms. The reaction can range from intense itching, redness, and swelling to the development of small, weeping blisters or raw, cracked skin.
Chronic inflammatory skin disorders can also produce changes easily mistaken for an infection. Lichen sclerosus is a long-term condition that causes the skin to become thin, white, and crinkled, often described as having a “cigarette paper” appearance. The affected skin is fragile and prone to developing painful tears, fissures, and bruising from minimal friction or scratching.
Lichen planus, another immune-mediated disorder, can affect the skin and mucous membranes, presenting as painful, shallow ulcers or reddish-brown patches on the vulva or penis. In some cases, a white, lacy pattern may be visible. The erosive form of the condition can be particularly severe, leading to significant pain and scarring.
How Doctors Determine the True Cause
Accurately determining the cause of a genital lesion relies on differential diagnosis, beginning with a thorough physical examination and detailed medical history. The clinician will closely inspect the appearance, size, location, and number of the lesions, noting whether they are painful, painless, soft, or firm, and if they are clustered or solitary. This visual assessment helps to narrow the possibilities from infectious and non-infectious causes.
Specific laboratory tests are then used to confirm or rule out common infectious agents. For an active lesion, a healthcare provider will typically use a swab to collect fluid or cells from the base of the sore for a Nucleic Acid Amplification Test (NAAT) or viral culture to check for HSV-1 and HSV-2 DNA. To test for a bacterial cause like syphilis, blood tests (serology) are performed to detect antibodies produced in response to the Treponema pallidum bacterium. For chronic or atypical lesions, a small tissue sample, or biopsy, may be taken and examined under a microscope to identify specific cellular changes indicative of a non-infectious dermatological condition.