Your gallbladder is like a little storage sac: It sits under your liver, collecting bile until the liquid is needed to help break down fats. After you eat fatty foods, your gallbladder contracts to pump bile into your small intestine for digestion. William Silverman, MD, a professor of medicine in the Division of Gastroenterology and Hepatology at the University of Iowa Hospitals and Clinics and the Iowa governor of the American College of Gastroenterology, says that when people develop a problem in this pear-shaped organ, it’s typically one of two things: “Gallstones, which are incredibly common, or gallbladder cancer, which is exceedingly rare.” Read on to learn more about both.

What exactly are gallstones?

In most cases, gallstones are small pieces of crystallized cholesterol. (The pebble-like lumps can form when there’s an imbalance of substances in the bile.) More than 25 million Americans have them—but most never even know it. Symptoms—and possibly infection—strike when the stones get stuck in the gallbladder’s narrow outlet, or in the ducts that drain the organ.

Women are more likely to get gallstones

This is especially true as we age. (Gallstones occur in almost a quarter of women by age 60.) It’s thought that the female hormone estrogen stimulates the liver to divert cholesterol into bile.

Pregnancy ups your risk. “During pregnancy you secrete the hormone progesterone in an increased amount and that decreases the gallbladder contraction,” explains Dr. Silverman. Bile lingering in the organ may become stagnant and stones may precipitate out.

Who else is at risk?

Certain populations are predisposed to gallstones, says Dr. Silverman, including the Pima Indians in Arizona. But most cases aren’t related to genetics, he says.

Waist size, however, does play a role: A large 2013 study published in Hepatology found that the higher a woman’s BMI, the more likely she was to develop gallstones.

Diabetes also raises a person’s risk, as well as bariatric surgery and extreme weight loss. (Gallstones are one of the reasons you should seek medical supervision when you hope to lose a large amount of weight.)

But the truth is, the majority of people who get gallstones don’t have any of the major known risk factors, says Dr. Silverman. “That would suggest that there are many things that we still really don’t understand.”

How are gallstones treated?

Sometimes doctors discover gallstones by accident while looking for something else. In that case it’s generally best to leave them alone. But if you’re experiencing symptoms, your doc will likely suggest cholescystectomy—an operation to remove the gallbladder (which may be done laparoscopically). Fortunately, the organ isn’t essential; once it’s gone, bile will flow directly from your liver to your small intestine.

Are there non-surgical options?

Oral medications are sometimes prescribed to patients who can’t undergo surgery, although it may take months or years for them to work, if they work at all.

In the 1980s, doctors began experimenting with a procedure called extracorporeal shock wave lithotripsy, which successfully pulverized gallstones using sound waves. But the treatment has since fallen out of use. “The stones would simply recur for whatever reasons caused them in the first place,” explains Dr. Silverman.

In the slides ahead you’ll find the most common signs of a gallbladder problem.

Symptom: Pain in the upper right abdomen

This is where your gallbladder is located, just beneath your liver. Sudden, extreme pain could mean that stones are causing a blockage: Your gallbladder may be contracting but unable to drain, “so pressure builds up and it hurts,” explains Dr. Silverman. But there are many other reasons you might experience pain in this area, he stresses, including muscle spasms. Call your doctor for emergency advice.

Sudden, intensifying pain in your intestines—located in the center of your abdomen—could also be a sign of gallstones.

Symptoms: Fever and chills with abdominal pain

A blockage by gallstones can cause a buildup of bile in the gallbladder, which may lead to an infection called cholecystitis. Pain, chills, and a fever of 100.4 degrees or higher are classic symptoms, and may come on after a big meal. There are a variety of ways to detect the problem, including blood tests and a scan that tracks the flow of bile. If you’re diagnosed, your MD will likely want to check you into the hospital. The treatment might involve fasting, antibiotics, and pain meds until the inflammation subsides.

Symptoms: A change in the color of your urine and stools

Bile salts are what make stools brown. If you noticed that your number-twos are pale or clay-colored, that might indicate that a gallstone is blocking the bile duct.

Your urine can also provide a clue. When there is excess bile building up in the body, it can turn your pee a darker, orange color.

Yellowing of your skin and eyes may occur as well. Read on for more about jaundice.

Symptom: Yellowing of the skin and eyes

Jaundice can by a sign of gallstones, but when it’s accompanied by abdominal pain and weight loss, it may be a symptom of gallbladder cancer. If a tumor is blocking the flow of bile, the yellow-brown fluid may build up in the body and give the skin and the whites of the eyes a yellow tint. Keep in mind, though, that jaundice is caused more often by hepatitis than cancer. In any case, it’s a good idea to see your doctor right away.

A sign you may need your gallbladder removed

Gallbladder polyps are growths on the inside of the gallbladder wall show up on ultrasounds, often when doctors are investigating unrelated problems. Most of the time, they’re nothing to worry about. But people with big polyps have a higher risk of developing gallbladder cancer, Dr. Silverman says: “I would emphasize that these are very large polyps, not tiny ones.” As a preventative measure, your doctor may recommend gallbladder removal.

What about gallbladder cancer?

People who have a history of gallstones or large polyps are more likely to develop gallbladder cancer—but even among this group, the risk is very small. The American Cancer Society estimates there are fewer than 11,000 cases diagnosed per year. Still, if you’ve dealt with gallbladder problems in the past and begin experiencing abdominal pain, bloating, itchiness, loss of fever, nausea, or unexplained weight loss, then make an appointment with your doctor.

This article originally appeared on Health.com

More from Health.com:

Get our Health Newsletter. Sign up to receive the latest health and science news, plus answers to wellness questions and expert tips. Please enter a valid email address. Sign Up Now Check the box if you do not wish to receive promotional offers via email from TIME. You can unsubscribe at any time. By signing up you are agreeing to our Terms of Use and Privacy Policy . This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply. Thank you! For your security, we've sent a confirmation email to the address you entered. Click the link to confirm your subscription and begin receiving our newsletters. If you don't get the confirmation within 10 minutes, please check your spam folder.

Contact us at letters@time.com.