Dear Doctor: My husband was in agony recently, and it turned out he was passing a kidney stone. Why does that hurt so much, and what can he do to keep it from happening again?

Dear Reader: It can be shocking, after passing a kidney stone, to see the relatively small size of the object that caused so much pain.

As the name suggests, kidney stones are hard, pebblelike objects formed from the minerals and salts found within the kidney. They can range in size from a grain of sand to a large marble. When stones leave the kidney, they pass into the ureter, which is the duct that carries urine to the bladder. The ureter can’t stretch to accommodate a foreign object, which makes the passage of larger stones difficult -- or even impossible. Pain from kidney stones often comes in waves because the ureter goes into spasm to try to force out the stone. When a stone reaches the junction where the ureter meets the bladder, it can cause a sharp, sometimes burning pain during urination.

When a kidney stone blocks the ureter, it causes a backup of urine into the kidney. The resulting pressure causes widespread pain and discomfort, including in the back, belly and groin. The blockage can also lead to infection, which adds fever and chills to the daunting list of symptoms. Nausea, vomiting, cloudy urine, smelly urine, blood in the urine and urinary urgency are also common symptoms. Treatment ranges from hydration and pain meds to make patients more comfortable while passing smaller stones to using shock wave therapy to break larger stones into particles small enough to pass to surgical options for difficult cases.

If you’ve had kidney stones, you can take steps to lessen the odds of a recurrence. First, drink plenty of water throughout the day. Hydrating dilutes your urine, inhibiting the growth of salts and minerals that may aggregate into stones. Also, avoid the use of a sauna, hot tub or steam bath; intensive and extensive workouts; a hot yoga class; and even relaxing on a hot summer day, which can result in sweating and loss of water that, in turn, leads to a drop in urine production. As you drink water during the day, you can add a generous squeeze of lime or lemon, both of which are high in natural citrate, a substance that helps prevent stone formation.

Be aware of your diet. The most common type of kidney stones are calcium stones, which are usually made up of calcium and oxalate, a chemical found in most foods. Foods high in oxalate include beets, spinach, peanuts, sweet potatoes, tea and chocolate.

Red meat, organ meats and shellfish are high in purines, which lead to a higher production of uric acid. This is tied to the formation of uric acid stones, another common type of kidney stone. Fructose, phosphate, salt and alcohol also play a role in kidney stone production. If this all sounds a bit overwhelming, consider asking your doctor to help you create a lifestyle plan to reduce your risk of getting kidney stones.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10880 Wilshire Blvd., Suite 1450, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)

Dear Doctor: Our summer is filling up with pool and beach activities, and though it’s great that our kids will get exercise and have fun, I’m also worried. The older boys are decent swimmers, but the youngest, who just turned 4, is still learning. How do we keep them all safe?

Dear Reader: Thank you for bringing up an important topic. With the hot (and hotter) weather and carefree summer vibe, water safety may not be the first thing on everyone’s minds. But according to statistics compiled by the Centers for Disease Control and Prevention, drowning is the leading cause of accidental death among children age 4 and younger. It’s the third-most-common cause of accidental death among children and adolescents between the ages of 5 and 19.

It’s great that your older kids can swim and that you’re making sure your youngest is learning. However, swimming skills alone aren’t enough to keep a child safe. As anyone who has spent time around kids at play knows, it’s basically chaos. That makes ensuring their safety around open water a daunting task. But the good news is that the basics of water safety fall into three manageable categories -- barriers, surveillance and education.

The American Academy of Pediatrics recommends -- and some local and state laws require -- that swimming pools be enclosed by a four-sided fence at least 4 feet high, with self-closing and self-locking gates with alarms. When swim time is over, doors facing the pool should remain locked. Let kids swim only in pools with clear water with good visibility, particularly near the dangerous area of the pool drain. At the ocean or a lake, set non-negotiable boundaries for where children can range. This includes not only water depth, but the width of the play area. That lets you create a manageable zone to watch them. An adult who can swim should always stay within arm’s length of any child with poor swim skills.

Vigilant surveillance is crucial. Even in areas with lifeguards, a designated adult should continually monitor kids in the water. No cellphones, no chatting, no daydreaming. As any parent whose child has gotten into trouble in the water can attest, the unthinkable happens in mere seconds. If you’re with other capable adults, break surveillance into shifts. When alone, give kids timed swim sessions. Regularly bring them onto dry land for snacks and sunscreen, and everyone gets a needed rest. Restate the physical limits of their play area each time they return to the water. If someone breaks the rules, the penalty is a non-negotiable return to dry land.

Education includes swimming and water competency lessons, which can begin as early as age 1. Learning CPR makes everyone safer. Studies show that kids as young as 9 can learn and use this vital skill. And learn the signs of drowning, which is actually a quiet event. Speech is secondary to breathing, and a drowning person may only have the ability to gasp for breath and try to stay afloat, and thus can’t cry for help. For information on water safety, visit poolsafely.gov.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10880 Wilshire Blvd., Suite 1450, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)

Dear Doctor: My best friend had a successful breast cancer surgery last spring. But the surgeon took out some lymph nodes, and now she’s getting lymphedema in her left arm. Is it true that there’s no cure?

Dear Reader: Lymphedema is the name for swelling that occurs when there is a blockage to the lymphatic system. Often, as in your friend’s case, it arises when lymph nodes are removed or damaged during cancer surgery or treatment. The condition can also be caused by infection, inflammation, injury or certain illnesses. Lymphedema is most common in the arms or legs, but it can occur anywhere in the body in which the lymphatic system is blocked. While there is no cure, recent developments in diagnostic tools offer hope for managing the condition.

The lymphatic system is a remarkable network of tissues, organs, ducts and nodes that collect and disperse lymph, or lymphatic fluid, throughout the body. If you’ve ever scraped yourself and noticed the clear fluid that seeps from the wound, that’s lymph. It’s made up of fats, proteins, white blood cells and cellular waste, and it is an integral part of the immune system.

The lymphatic vessels that transport lymph throughout the body have valves that keep the fluid moving in one direction. But unlike our circulatory system, which utilizes the heart to move blood through the body, the lymphatic system has no central pump. Instead, it relies largely on the movement of skeletal muscles to keep lymph moving. Lymph vessels carry the lymphatic fluid throughout the body and eventually to the lymph nodes -- hundreds of small, round structures that collect the fluid and filter out the waste and bacteria it carries. When enough lymph nodes are damaged or removed, that part of the lymph system is blocked. The result is that fluid collects and causes the swelling known as lymphedema.

The condition can be painful; it can result in tissue damage and infection, and often limits a person’s range of motion in the affected limb. At this time, treatment focuses on managing swelling and pain. This includes the use of compression garments, physical therapy and lymphatic massage, a technique performed by trained specialists to manually disperse the accumulated lymphatic fluid. Strides are also being made in microsurgery, including lymph node transfer and the repair of lymph vessels.

More recently, a diagnostic technique called bioimpedance spectroscopy, which uses an electric current to measure the buildup of extracellular fluid, is seen as a potential advance in the early detection of lymphedema. This is important because the sooner that patients begin lymphedema therapies, the better the condition can be controlled. Last year, small studies into the use of certain anti-inflammatories to manage swelling also showed promise.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10880 Wilshire Blvd., Suite 1450, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)