Low Grade Squamous Intraepithelial Lesion (LSIL) of the Vulva: Understanding Your Pathology Report

By Jason Wasserman MD PhD FRCPC
May 22, 2026

Low grade squamous intraepithelial lesion (LSIL) of the vulva is a noncancerous change in the skin of the vulva caused by infection with human papillomavirus (HPV). It is made up of squamous cells that have been infected by the virus and show mild abnormal changes, a pattern pathologists call dysplasia. These changes are confined to the top layer of the vulvar skin (the epidermis), which is why the condition is called “intraepithelial.”

LSIL is the least severe form of HPV-related change and is not cancer. In most people, the immune system clears the HPV infection, and the affected skin returns to normal on its own. LSIL of the vulva was previously referred to as “vulvar intraepithelial neoplasia 1 (VIN1)” or “flat condyloma.” It is distinct from high grade squamous intraepithelial lesion (HSIL) of the vulva, which carries a meaningfully higher risk of progressing to cancer. The same type of change can also occur in the cervix, vagina, and anal canal.

This article will help you understand what this diagnosis means on your pathology report, what each term means, and why it matters for your care.

What causes LSIL of the vulva?

LSIL of the vulva is caused by infection with HPV, a very common virus that spreads through skin-to-skin contact, including sexual contact. Most HPV infections clear on their own within one to two years. While the infection is present, the virus can cause mild changes in the squamous cells that are recognized as LSIL.

LSIL can be caused by both low-risk and high-risk HPV types:

Low-risk HPV types — Types such as HPV6 and HPV11 commonly cause LSIL and genital warts. These types very rarely lead to cancer.
High-risk HPV types — Types such as HPV16 and HPV18 can also cause LSIL. While most LSIL caused by high-risk HPV still resolves on its own, the presence of a high-risk type is one of the factors a doctor considers when deciding how closely to monitor the condition.

Several factors increase the chance of developing LSIL or of having an infection that persists rather than resolving, including a weakened immune system (from conditions such as HIV infection or immunosuppressive medication), cigarette smoking, and not having received the HPV vaccine.

What are the symptoms?

Many people with LSIL of the vulva have no symptoms, and the condition is found by chance during an examination performed for another reason. When LSIL does cause noticeable changes, they may include:

Visible bumps or warts — LSIL is sometimes associated with genital warts (condyloma), which appear as soft, raised, skin-colored growths on the vulva.
Flat or slightly raised patches — The affected skin may show flat areas that look slightly different in color or texture from the surrounding skin.
Mild itching or irritation — Some people notice mild itching or discomfort, although many have no symptoms at all.

Because LSIL often causes no symptoms, it is frequently discovered only when a biopsy is taken to evaluate a visible change or another concern.

How is the diagnosis made?

The diagnosis of LSIL of the vulva is made when a sample of vulvar skin is examined under the microscope by a pathologist. The sample is usually obtained through a small biopsy taken from the area of concern during an office visit. The biopsy confirms the diagnosis and, importantly, allows the pathologist to ensure the changes are limited to LSIL rather than a more advanced condition such as HSIL.

To help distinguish LSIL from HSIL and other conditions that may appear similar, the pathologist may perform a special test called immunohistochemistry for the protein p16. In LSIL, p16 is typically negative or shows only patchy staining. This is different from HSIL, which usually shows strong, continuous “block-type” p16 staining. The p16 result helps confirm that the changes are low-grade.

What does LSIL of the vulva look like under the microscope?

Under the microscope, LSIL of the vulva shows mild changes in the squamous cells that are confined to the lower part of the epidermis (the top layer of the vulvar skin). The features include:

Koilocytes — Koilocytes are squamous cells that have been infected by HPV. They are larger than normal and have an irregular, dark nucleus surrounded by a clear space, or “halo.” Koilocytes are a hallmark of LSIL.
Mild changes confined to the lower epidermis — The abnormal cells are limited to the lower one-third of the epidermis. The cells in the upper layers appear mature and organized. This limited extent is what makes the changes “low grade.”
Negative or patchy p16 — LSIL is typically negative or only patchy for the protein p16, in contrast to the strong, continuous “block-type” staining seen in HSIL.
No invasion — The abnormal cells stay confined to the top layer of the skin and do not invade into the deeper tissue. LSIL cannot spread to other parts of the body.

What is the prognosis?

The prognosis for LSIL of the vulva is excellent. LSIL is the mildest form of HPV-related change, and it is best understood as a sign of an active HPV infection rather than a true precancer. Most cases resolve on their own within one to two years as the immune system clears the underlying HPV infection. The risk of LSIL progressing to vulvar cancer is very low, and substantially lower than the risk associated with HSIL.

A few factors influence whether LSIL resolves or persists:

HPV type — LSIL caused by low-risk HPV types very rarely progresses. LSIL caused by high-risk HPV types still usually resolves, but may be monitored more closely.
Immune status — People with a weakened immune system are more likely to have HPV infections that persist, and therefore LSIL that persists.
Smoking — Continued smoking is associated with reduced clearance of HPV infection.

What happens after this diagnosis?

Because LSIL of the vulva is a mild condition that usually resolves on its own, treatment is often not needed. The discussion between you and your doctor about next steps depends on whether you have symptoms, whether visible warts are present, and your overall situation.

Options that the team may discuss include:

Observation — For LSIL without bothersome symptoms, the most common approach is to monitor the area over time, since most LSIL resolves without treatment. Your doctor may recommend a follow-up examination after a defined interval.
Treatment of genital warts — If LSIL is associated with bothersome genital warts, the team may discuss treatments such as topical medications, freezing (cryotherapy), or other procedures to remove the warts. These treatments address the warts but are not required to “cure” the underlying LSIL.
Follow-up examination — Because HPV can affect more than one area of the lower genital tract, your doctor may recommend examination of the cervix, vagina, and surrounding skin, and continued cervical cancer screening on the usual schedule.
HPV vaccination — If you have not already received it, the team may discuss it. Vaccination does not treat an existing LSIL, but it can lower the risk of acquiring new HPV infections.
Smoking cessation — If you smoke, stopping is associated with improved clearance of HPV infection.

Most people with LSIL of the vulva do not require any specific treatment, and the condition resolves on its own. Your doctor will let you know whether any follow-up is needed based on your individual situation.

Questions to ask your doctor

Was LSIL the only finding on my biopsy, or were other changes present?
Was HPV testing performed, and if so, was a low-risk or high-risk type identified?
Was p16 testing performed, and what did the result show?
Do I need any treatment, or is observation the best approach for me?
If I have genital warts, what are my options for treating them?
How likely is it that this LSIL will resolve on its own?
Do I need follow-up examinations, and if so, how often?
Should I be checked for HPV-related changes in my cervix, vagina, or other areas?
Should I be vaccinated against HPV if I have not already been vaccinated?
What symptoms or changes should prompt me to contact you?