Short answer
Genital-rash comparison runs two rosters, STI patterns (syphilis, herpes, scabies) against dermatologic ones (dermatitis, yeast, psoriasis, lichen disorders), decided by distribution mapping (where exactly, including palms, soles, and extragenital skin), exposure and product histories, and targeted testing.
The method treats the identified cause rather than the itch alone, which is why the exam covers the whole skin, not just the complaint.
Continue with Genital Rash: Possible Causes and When to Get Care and Genital Sores: Causes and Evaluation for the directly connected guidance.
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See Tests & Prices →STI patterns in detail
- Secondary syphilis: diffuse, typically non-itchy rash that classically includes palms and soles, plus mucous patches, patchy hair loss, and swollen nodes. The “great imitator” earning its name. Blood testing confirms; appearance never does.
- Herpes: grouped painful blisters becoming shallow ulcers, recurring at the same sites, sometimes with burning urination or groin tenderness.
- Scabies: thin burrow lines with nighttime-predominant itching, often affecting household or sexual contacts simultaneously. Simultaneous spread is itself diagnostic evidence.
Dermatologic patterns in detail
- Irritant/allergic contact dermatitis: onset tracking a new soap, pad, detergent, latex product, or lubricant. Product timelines diagnose.
- Candidiasis: moist-fold redness with satellite pustules, worse with diabetes or recent antibiotics.
- Psoriasis: sharply demarcated red plaques with silvery scale, with extragenital plaques (elbows, knees, scalp) coexisting.
- Lichen planus/sclerosus: violaceous polygonal papules or white crinkled patches with architectural change. Biopsy thresholds apply, and potent steroids need diagnosis first, not last.
Evaluation sequence that works
Full-skin examination first. Extragenital clues (palms, soles, elbows, nails, scalp) decide many genital rashes before genital testing begins.
Then three histories: sexual exposures, new products, new medications.
Then targeted testing: syphilis serology for diffuse rashes, herpes NAAT swabs for vesicles, skin scrapings for burrows or scale, glucose screening for recurrent candidiasis, biopsy for atypical persistence.
Each step narrows; skipping to creams widens.
Treatment follows identification
Syphilis gets stage-based penicillin; herpes gets episodic or suppressive antivirals; scabies gets whole-household treatment; dermatitis gets irritant removal; yeast gets antifungals; psoriasis/lichen get dermatologic management.
Same itch, six different cures. The evaluation is the treatment’s prerequisite.
When to seek care
Promptly for rashes with sexual exposure, palm/sole involvement, vesicles, burrow patterns, or ulceration.
Routinely for persistent rashes failing two weeks of appropriate basic care.
With biopsy advocacy for chronic, atypical, pigmented, or architecturally changing lesions.