They’re usually just a few millimeters in size, but they can be oh-so-painful. We’re talking about stones — gallbladder stones (or gallstones) and kidney stones, that is. They form in different systems of the body, but they’re similar in many ways. For example, both gallstones and kidney stones are common and can exist inside your body without causing any problems. They won’t cause pain or require treatment unless they get big enough to block the regular flow of fluids in their respective bodily systems.

Kidney Stones:

Where they develop: Urinary tract. They can be as small as a grain of sand and can grow up to several centimeters in diameter.

How big are they? Can be as small as a grain of sand, and can grow up to several centimeters in diameter.

They cause pain when: They move through the urinary tract (into the ureter) and block the flow of urine.

Where it hurts: Blood in the urine, painful urination, inability to urinate, or frequent urination. Often accompanied by nausea, vomiting, fever, or sweating.

Who’s at risk? Kidney stones are most common in middle-aged adults. Increased risk for people who have a family history of kidney stones, very low urine output, or other health conditions that affect the levels of certain substances in the urine.

Foods that contribute: A diet high in sodium, oxalates, or animal protein. Insufficient intake of fluids or calcium.

Treatment: Smaller stones (<10mm) may pass on their own, or with the help of medications that can relax the ureter. A number of minimally invasive surgical options are also available.

Can you get them again? Yes, many people have recurrent kidney stones. The risk of forming more stones is actually higher than the first-time risk for the general population.