Several STIs can cause vulvar itching, sores, or swelling, most often genital herpes (painful blisters and sores), trichomoniasis (itching with frothy discharge), and pubic lice (itching plus visible nits). But a vaginal yeast infection, eczema, lichen sclerosus, and contact dermatitis cause the same complaints and aren't sexually transmitted. A test tells them apart; the symptom won't.
painful blisters that crust over; tends to recur
thick white discharge, intense itch (not an STI)
frothy, itchy discharge with an odor
itching with visible lice or nits in coarse hair
| Item | Value |
|---|---|
| Genital herpes | managed — painful blisters that crust over; tends to recur |
| Vaginal yeast infection (candidiasis) | curable — thick white discharge, intense itch (not an STI) |
| Trichomoniasis | curable — frothy, itchy discharge with an odor |
| Pubic lice (crabs) | curable — itching with visible lice or nits in coarse hair |
The short list of likely causes
The vulva is the external female genital area, so symptoms you see and feel there — itching, sores, swelling, soreness — come from a mix of infections and skin conditions. When an STI is the cause, the usual suspects are genital herpes, trichomoniasis, and pubic lice. A yeast infection is extremely common but isn't usually sexually transmitted. A fair number of cases turn out to be ordinary skin problems rather than an infection at all. These overlap too much to sort out by looks alone, and several are frequently silent.
Which STIs cause vulvar symptoms
Genital herpes
Genital herpes is caused by two viruses, herpes simplex virus type 1 (HSV-1) and type 2 (HSV-2) CDC, About Genital Herpes. Its tell-tale pattern is sores. A first outbreak starts as small blisters that break open into painful sores, which take a week or more to heal, sometimes with flu-like symptoms — fever, body aches, and swollen glands in the groin. Sores can appear on or around the genitals, the rectum, or the mouth. Later outbreaks tend to be shorter and milder, and many people feel a warning prodrome (tingling or itching) a day or so before a sore appears.
Most people who carry herpes have no symptoms or very mild ones, don't know they're infected, and the majority of HSV-2 infections go undiagnosed. No blisters does not mean no herpes. If you want options for managing the virus long-term, our guide to alternative herpes treatments walks through what's realistic and what isn't.
Vaginal yeast infection (candidiasis)
A yeast infection is a fungal infection, usually from Candida albicans, and it's one of the most common fungal infections there is CDC, About Candidiasis. It is not usually acquired through sex, so it isn't classed as an STI. The classic vulvar pattern is itching or soreness with a thick, white discharge, sometimes pain during sex or a burn when you urinate. Most cases are mild, but a bad one brings real redness, swelling, and even small cracks in the skin. That picture overlaps closely with other infections, so our full rundown of yeast infection symptoms is worth a look before you assume that's what it is.
Trichomoniasis
Trichomoniasis is caused by a tiny parasite, Trichomonas vaginalis, and it's the most common curable STI CDC, About Trichomoniasis. About 70% of infected people have no symptoms at all. When women do get them, the pattern is itching, burning, redness or soreness of the genitals, discomfort urinating, and a clear, white, yellowish, or greenish discharge that often smells fishy. Symptoms, when they show up, can appear anywhere from about 5 to 28 days after infection, but sometimes much later, so timing alone won't tell you who passed it to whom. If trich is on the table, see how it's confirmed in our page on trichomoniasis testing & diagnosis.
Pubic lice (crabs)
Pubic lice — "crabs" — are Pthirus pubis, small insects that feed on blood and live in coarse pubic and perianal hair, and occasionally the armpits, chest, beard, or eyelashes CDC, About Pubic Lice. They spread mostly through sexual contact. Many infestations cause nothing at all; when symptoms do occur, you'll get itching in the genital area plus lice or nits (eggs) you can actually see stuck to pubic hair, sometimes with sores from scratching. Unlike herpes or trich, this one you can often confirm by eye. The full picture is in our guide to crabs symptoms.
When it's NOT an STI
Plenty of vulvar symptoms have nothing to do with sex. The big three non-STI culprits are eczema (an itchy, inflamed skin reaction), lichen sclerosus (a chronic condition that thins and whitens vulvar skin and can cause cracking and scarring), and contact dermatitis (irritation from soaps, detergents, wipes, lubricants, or new underwear). A yeast infection belongs in this group too. An itchy, sore, swollen vulva looks similar whether the cause is an allergen, a fungus, or a virus, so guessing fails often.
How to tell them apart
There are clues, even if none are proof. Painful blisters that crust over point toward herpes. Visible bugs or nits on the hair point toward lice. Thick, white, cottage-cheese discharge leans yeast; a frothy, fishy, greenish discharge leans trichomoniasis. Skin that's chronically white, thin, or cracked without discharge suggests a skin condition like lichen sclerosus rather than an infection. But these patterns blur, several causes are commonly silent, and people frequently have more than one thing at once. A test is what settles which one it is, if any.
| Cause | STI? | Tell-tale vulvar pattern | How it's confirmed |
|---|---|---|---|
| Genital herpes | Yes | Painful blisters that break into sores; possible flu-like symptoms | Swab of a lesion (NAAT or culture) |
| Trichomoniasis | Yes | Itching, burning, frothy yellow-green fishy discharge | NAAT on a vaginal swab or urine |
| Pubic lice | Yes | Genital itching with visible lice/nits on hair | Seeing a louse or nits by eye |
| Yeast infection | Usually no | Itching, soreness, thick white discharge | Microscope wet prep / fungal culture; normal pH |
| Eczema / contact dermatitis | No | Itchy, inflamed skin, often after a new product | Skin exam, history |
| Lichen sclerosus | No | White, thin, cracked skin; chronic itch | Skin exam, sometimes biopsy |
How it's tested
Testing depends on what's suspected: a swab of a sore for herpes CDC, Herpes Testing, a NAAT on a vaginal swab or urine for trichomoniasis CDC, 2021, a microscope look at discharge for yeast CDC, Candidiasis, and a simple naked-eye exam for lice CDC DPDx. In practice that means a urine sample, a self-collected swab, or a quick exam — often free or low-cost at health departments, Planned Parenthood, and Title X clinics, with results usually back in a few days. When you're ready, here's how to get tested, and if your exposure was recent, check when to test after exposure so you don't test too early.
What to do next
Once you have a diagnosis, treatment is usually straightforward and depends on the cause — antiviral pills for herpes, a single course of medication for trichomoniasis, an antifungal for yeast, and a topical treatment for lice. Don't keep treating yourself for yeast when the real problem is something else; if a drugstore antifungal hasn't worked, get checked rather than repeat it.
Red flags — when to get seen urgently
- You have spreading redness, increasing swelling, fever, or sores that look infected (pus, worsening pain) — signs the area needs prompt care.
- A first herpes-like outbreak with severe pain or trouble urinating, which can be intense enough to need same-week treatment.
- You're pregnant and develop any new genital sores, discharge, or itching.
- Sores that don't heal, or white, thinning, scarring skin that keeps coming back — that pattern needs a skin exam, not another antifungal.
- Symptoms after a recent new partner or assault, where early testing and care matter.