It comes quickly, and it's not quickly forgotten. Ouch, the pain!

Some say few kinds of pain can outdo the agony of a kidney stone. The pain strikes in waves in the lower back or right on the side of the trunk, around the bottom rib.

Often, it's accompanied by sweating, vomiting and nausea, blood in the urine and the urgent need to go to the bathroom.

"The good news is that most stones pass on their own," says Jeffry Huffman, M.D., urologist at the University of Southern California (USC). That generally happens within a day or two of the onset of pain, bringing relief to the stones' unwary hosts.

Kidney stones usually form in the center of the kidney, on the ends of collecting tubules. That's where the kidney drains out its wastes into tiny tubes, which lead down into the ureter and finally into the bladder. Little stones can break off and leave the body easily in urine.

But bigger stones can irritate the ureter and get stuck as they move toward the bladder, prompting that infamous pain and interfering with urine flow. The stones form when certain natural chemicals in urine crystallize and the crystals clump together. Calcium is the culprit in most cases of kidney stones, Huffman says.

Many stones are caused by metabolic problems or the way the body deals with foods or drinks in the diet, such as tea. Uric acid, phosphate and other substances also may cause stones.

But because patients usually end up in the emergency room with severe pain, and an infection may accompany the condition, doctors usually treat the symptoms and any disease before trying to figure out the underlying causes of a person's kidney stone.

Stones most frequently occur to people in their 20s and 30s, and tend to occur more in men than women. They can be an inherited condition, Huffman says, "and half of all people with a stone will get another stone within seven years."

People living in equatorial countries, as well as the southwest and southeast United States, are more likely to get stones, since those are hot areas where people are more likely to be dehydrated, Huffman says. The best way to avoid stones?

Drink two to three liters of water-eight to ten glasses-each day, he suggests.