Sure, not every woman is walking around with an itchy vagina, but many are. Below-the-belt itching is “a common symptom that we see as gynecologists. It can be so bothersome that even mild symptoms will bring women in,” said Julianna Schantz-Dunn, MD, an ob-gyn at Brigham and Women’s Hospital in Boston.

And the reasons why can range from benign (your choice of undies) to more worrisome (an STI).

That’s why it’s important to figure out what the heck’s going on. That, and it’s not like you can go around scratching your crotch all day.

While you don’t have to run to the doc for every unusual itch, she recommends making an appointment if symptoms stick around for more than two days or if, along with the scratchiness, you have unusual bleeding or lesions in the area.

Here are seven possible causes, plus the best advice for fixing each one.

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Yeast infection
We’ll start with the most obvious one: yeast. These infections are so common that three-fourths of women will get one at some point. The hallmark symptom is extreme itchiness, along with an odorless thick, white discharge.

“We suggest you at least call your doctor to discuss your symptoms rather than going to the drugstore to buy an OTC treatment,” Schantz-Dunn said. “If you randomly self-treat and it’s not a yeast infection, you can make the problem worse,” she said.

Trichomoniasis
This common sexually transmitted infection (STI) is caused by a parasite called Trichomonas vaginalis. The U.S. Centers for Disease Control and Prevention (CDC) notes that while 3.7 million people are infected (more of them women), only 30 percent know it. That’s because it often causes no symptoms. But when it does, it causes itching, burning, a change in discharge, or external white cracking in the skin, Shantz-Dunn said.

“You may assume it’s a yeast infection and try an OTC antifungal, and it doesn’t work. Then you try douching, [which is never a good idea], and that makes it worse,” she added.

That’s all the more reason to see your doc first. If tests come back positive, it’s very easy to cure with an antibiotic, but the catch is both you and your partner have to be treated, otherwise, you can easily re-infect each other.

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Irritation
Rounding out the top three most common causes, Schantz-Dunn says, is irritation caused by certain fabrics or products.

“We often talk to patients about good vulvar hygiene,” she said.

That includes not wearing scented panty liners (and not wearing panty liners too much overall), avoiding scented soaps for down-there cleaning, and absolutely never douching or using scented feminine sprays or powders. These can kickstart the problem; then, scratching can lead to infection, making things worse. Besides, these can also change up the pH of the vagina, making you more susceptible to an infection called bacterial vaginosis (BV). (More on that later.)

Also, your vagina needs to breathe. Suffocating it with synthetic underwear traps moisture against your skin, which can be an irritant. Switch to cotton, Schantz-Dunn recommended. And be sure you’re gently washing up with regular, unscented soaps around the outside only.

Bacterial vaginosis
While this vaginal infection can cause some itching, Schantz-Dunn warned that more often the hallmark symptom of BV is a foul-smelling discharge. If you call your doc and explain that you itch like crazy, he or she will more likely think it points to a yeast infection, trichomoniasis, or irritation, she says. So be sure to make note of all your symptoms, including details about discharge, which can go a long way in identifying your issue.

Herpes
You may think you could spot genital herpes, but not everyone gets big lesions that are easy to see.

“You may feel some itching or painful urination, but the symptoms may not be as severe as you’d think,” Schantz-Dunn said. “I’ve seen people try to treat herpes with a topical yeast medication—and that doesn’t do much.”

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A shaving disaster
When you shave down there, it may feel smooth in the moment, but when the hair grows back it’s itchy city. In fact, in a 2014 study published in the American Journal of Obstetrics and Gynecology about problems women experience ridding public hair, 20 percent said they’ve felt severe itching.

“Women know their bodies well and if they know they get irritated from shaving, I say don’t do it,” Schantz-Dunn noted.

A vagina-friendlier way: trim the hair or get a bikini wax.

Hormones
If you’re post-menopausal, the source of the itch could be that your vagina is changing along with your changing hormones. Namely, a drop in estrogen can thin the mucosal lining in your vagina. But don’t fret: after ruling out other causes, “we can treat this with a vaginal estrogen cream or tablet,” Schantz-Dunn said.

This article originally appeared on Health.com.