JAUNDICE

In the first few days of life, more than half of all full-term babies and as many as 80 percent of premature infants who are otherwise healthy develop jaundice, a yellowish discoloration of the skin and eyes. Although some babies are jaundiced at birth, most develop the condition during the second or third day of life. That's why you may not notice it until after your baby is home.

Jaundice itself isn't a disease. In most cases it occurs because your baby's liver isn't mature enough to metabolize a molecule called bilirubin, which normally forms when the body recycles old or damaged red blood cells.

Jaundice usually isn't a cause for alarm. It doesn't cause discomfort for your baby and most often disappears on its own in one to two weeks. Still, it should be closely monitored by your baby's doctor because severe jaundice can lead to serious complications. Phototherapy, a treatment using special ultraviolet lights, can help keep your baby's blood level of bilirubin from becoming too high.

KIDNEY CANCER

Your kidneys are two bean-shaped organs, each about the size of your fist. They're located behind your abdomen, one on each side of your spine. Like other major organs in your body, your kidneys can sometimes develop cancer. In adults, the most common type of kidney cancer is renal cell carcinoma (renal adenocarcinoma or hypernephroma), which begins in the cells that line small tubes (tubules) within your kidneys. Children are more likely to develop a kind of kidney cancer called Wilms' tumor.

Kidney cancer seldom causes problems in its early stages. But as a tumor grows, you may notice blood in your urine or experience unintentional weight loss or back pain that doesn't go away. Cancer cells may also spread (metastasize) outside your kidneys to nearby organs such as your adrenal glands, pancreas and spine, as well as to more distant sites in your body.

An estimated 35,000 Americans are diagnosed annually with kidney cancer and more than 12,000 die of the disease. Yet if kidney cancer is detected and treated early, the chances for a full recovery are good.

KIDNEY FAILURE

Your kidneys are two bean-shaped organs, each about the size of your fist. They're located at the back of your upper abdomen, one on either side of your spine. The kidneys' main function is to eliminate excess fluid and waste material from your blood. When your kidneys lose their filtering ability, dangerous levels of fluid and waste accumulate in your body — a condition known as kidney (renal) failure.

Sometimes kidney failure happens suddenly (acute kidney failure). This is most likely to occur after complicated surgery or a severe injury, or when blood vessels leading to your kidneys become blocked.

Chronic kidney failure, on the other hand, usually develops slowly, with few signs or symptoms in the early stages. Many people with chronic kidney failure don't realize they have a problem until their kidney function has decreased to less than 25 percent of normal. High blood pressure and diabetes — a disorder that causes high blood sugar levels — are the most common causes.

In end-stage renal disease, the kidneys function at less than 10 percent of normal capacity. At this point they simply can't sustain life. People with end-stage renal disease need either dialysis or a kidney transplant to stay alive. When a transplant isn't possible — often because of poor general health — dialysis becomes the only option

KIDNEY STONES

If you've ever passed a kidney stone, you're not likely to forget the experience — it can be excruciatingly painful. What's more, kidney stones (renal lithiasis) are increasingly common. One in 10 Americans will have at least one kidney stone some time in their life.

Not all kidney stones cause symptoms. They're often discovered when you have X-rays for an unrelated condition or when you seek medical care for problems such as blood in your urine or recurring urinary tract infections. The pain becomes agonizing only when a stone breaks loose and begins to work its way down from your kidneys to your bladder.

Kidney stones usually form when your urine becomes too concentrated. This causes minerals and other substances in urine to form crystals on the inner surfaces of your kidneys. Over time, these crystals may combine to form a small, hard mass, or stone.

Most small kidney stones pass into your bladder without causing any permanent damage. Still, it's important to determine the underlying cause so that you don't form more stones in the future. In many cases, you can prevent kidney stones simply by drinking more water and making a few dietary changes.

LACTOSE INTOLERANCE

The simple pleasure of drinking a cold glass of milk or eating a slice of cheesy pizza can turn into a painful exercise if you're one of the 30 million to 50 million Americans who have lactose intolerance. This common condition means you aren't able to fully digest the milk sugar (lactose) in dairy products. It usually isn't dangerous, but the symptoms can be distressing enough to make you want to steer clear of the dairy aisles.

The underlying problem is a lack of lactase — an enzyme produced by your small intestine, which breaks down lactose in preparation for absorption into your bloodstream. Lactase deficiency leads to problems in breaking down and absorbing milk sugar (lactose malabsorption).

Some people who believe they are lactose intolerant actually don't have impaired lactose digestion. And not everyone with low levels of lactase is lactose intolerant. Only people with low lactase levels and symptoms are considered lactose intolerant.

In addition, intolerance to a food isn't the same as a food allergy. Lactose intolerance doesn't involve your immune system and doesn't necessarily require complete avoidance of milk products. You can control symptoms of lactose intolerance through a carefully chosen diet that limits lactose without cutting out calcium.

LARYNGITIS

Laryngitis is an inflammation of your voice box (larynx) due to overuse, irritation or infection. The larynx is a framework of cartilage, muscles and mucous membranes that forms the entrance of your windpipe (trachea). Inside the larynx are your vocal cords — two folds of mucous membrane covering muscle and cartilage.

Normally, your vocal cords open and close smoothly, forming sounds through their movement and vibration. But when your vocal cords become inflamed or irritated, they swell, causing distortion of the sounds produced by air passing over them. As a result, your voice sounds hoarse. In some cases, your voice can become so faint as to be undetectable.

Laryngitis may be short-lived (acute) or long-lasting (chronic). Although acute laryngitis usually is nothing more than an irritation, persistent hoarseness can signal a more serious problem.

LEUKEMIA

Leukemia is cancer of your body's blood-forming tissues, including the bone marrow and lymph system. The word leukemia means "white blood" in Greek. The disease usually starts in the white blood cells.

Under normal circumstances, your white blood cells are potent infection fighters. These cells normally grow and divide in an orderly, controlled way, as your body needs them. But leukemia disrupts this process.

In people with leukemia, the bone marrow produces a large number of abnormal white blood cells. They look different from normal blood cells and don't function properly. Eventually, they block production of normal white blood cells, impairing the ability to fight off infection. Leukemia cells also crowd out other types of blood cells produced by the bone marrow, including red blood cells, which carry oxygen to tissues throughout the body, and platelets, which help form blood clots that control bleeding.

Leukemia isn't just a children's disease, as some people think. Leukemia has four main types and many subtypes — and only some of them are common among children. Overall, this form of cancer affects about 10 times as many adults as children. New cases of leukemia number more than 30,000 annually in the United States. Leukemia is usually fatal without successful treatment

LICE

Lice are tiny, wingless, parasitic insects that feed on your blood. This itchy infestation is easily spread — especially by school children — through close personal contact and by sharing personal belongings.

Several types of lice exist:

• Head lice. These lice develop on your scalp. They're easiest to see at the nape of your neck and over your ears. Small eggs (nits), produced by lice, attach to your hair shafts. The eggs hatch in about one week, resulting in more lice.
  
  
• Body lice. These lice spend most of their time in the seams and folds of your clothing. Body lice are often spread by direct contact with infected clothing or bedding or with an infected person. In rare cases, body lice may carry diseases.
  
  
• Pubic lice. Commonly called crabs, these lice occur on the skin and hair of your pubic areas and on eyelashes. Sexual contact or contact with infected clothing, bedding or even toilet seats can spread pubic lice.

You or your child can have good personal hygiene habits and still get lice. Unless treated properly, this vexing condition can become a recurring problem.

LIVER CANCER

Primary liver cancer occurs when cancerous (malignant) cells begin to grow in the tissues of your liver. Although many cancers are on the decline, the incidence of primary liver cancer in the United States increased more than 70 percent between 1975 and 1995. The increase is linked to rising rates of hepatitis B and C infection — the leading causes of liver cancer.

Far more common than primary liver cancer, however, is cancer that occurs when tumors from other parts of the body spread (metastasize) to the liver. The liver is especially vulnerable to invasion by tumor cells and with the exception of the lymph nodes, is the most common site of metastasis.

Because liver cancer is rarely discovered early, the prognosis is often poor. Yet even in advanced cases, treatment can help relieve symptoms and improve quality of life. In addition to standard treatments such as surgery, chemotherapy and radiation, new and less invasive therapies may be an option for some people.

But the most encouraging news about liver cancer is that you can greatly reduce your risk by receiving a vaccine that protects you from the hepatitis B virus (HBV). Lifestyle changes can help prevent other major causes of liver cancer, such as hepatitis C and cirrhosis.

LOCKJAW

Tetanus is a serious bacterial disease that leads to stiffness of your jaw muscles and other muscles. It can cause severe muscle spasms, make breathing difficult and, ultimately, threaten your life.

A cut, puncture wound, laceration or other wound can lead to a tetanus infection and toxin production in someone without immunity. Spores of the tetanus bacteria, Clostridium tetani, usually are found in the soil but can occur virtually anywhere. If deposited in a wound, the bacteria can produce a toxin that interferes with the nerves controlling your muscles.

Treatment is available, but the process is lengthy and not uniformly effective. Tetanus may be fatal despite treatment. The disease is rare in the United States, with about 100 cases being reported annually. A small number of those result in death. The number of cases and resulting deaths is far higher in developing countries. The best defense against tetanus is prevention.

LOW BLOOD SUGAR

Hypoglycemia is a condition caused by an abnormally low level of blood sugar (glucose) , your body's main energy source.

Hypoglycemia affects about one out of every 1,000 people in the United States, many of whom have diabetes. However, a wide variety of health conditions, many of them rare, can cause low blood sugar in people without diabetes. Like fever, hypoglycemia is merely an indicator of a health problem.

Among the underlying causes of hypoglycemia in people without diabetes are certain medications, alcohol, certain cancers, critical illnesses including kidney, liver or heart failure, hormonal deficiencies, and disorders that result in your body producing too much insulin. Insulin is the hormone secreted by your pancreas that regulates your level of blood sugar.

Treatment of hypoglycemia involves short-term steps to get your blood sugar level back into a normal range and long-term steps by your doctor to identify and treat the underlying cause.

LUNG CANCER

Lung cancer is the leading cause of cancer deaths in the United States, among both men and women. It claims more lives than colon, prostate and breast cancer combined. Since the mid-1990s, more than 150,000 Americans have died of the disease each year.

Yet most of these deaths could have been prevented. That's because smoking accounts for about 85 percent to 90 percent of lung cancer cases. Although your risk of cancer increases with the length of time and number of cigarettes you smoke, quitting smoking, even after many years, can greatly reduce your chances of developing the disease.

Protecting yourself from exposure to other leading causes of lung cancer, such as asbestos, radon and secondhand smoke, also decreases your risk. Prevention is especially important because lung cancer usually isn't discovered until it's at an advanced stage when the outlook for recovery is less positive.

Treatment for lung cancer depends on the type of cancer, how advanced it is and your overall health. In some cases, surgical removal of the tumor may be an option. In others, chemotherapy, radiation or a combination of the two is likely to provide better results.

LUPUS

Lupus is a chronic inflammatory autoimmune disease that can affect many parts of your body, including your skin, joints, kidneys, blood cells, heart and lungs. Episodes of lupus tend to come and go throughout your life, and they may make you feel tired and achy.

Lupus occurs in several types, including systemic lupus erythematosus (SLE), discoid and drug-induced. SLE is the most common type and causes the most difficulties. It can lead to problems such as fever, swollen joints, anemia and kidney failure. Lupus is most commonly diagnosed when people are between 15 and 45 years old.

According to the Lupus Foundation of America, the disease affects about 1.5 million Americans, and most of them are women. Blacks, Hispanics, Asians and Native Americans are two to three times as likely as whites to have lupus.

The diagnosis and treatment of lupus has improved tremendously in the past few decades. If you take care of yourself and get proper medical treatment, you usually can still lead an active, healthy life.

LYME DISEASE

Lyme disease is an infectious illness caused by the bacterium Borrelia burgdorferi. It's transmitted mainly through tick bites. The disease was identified in 1975 in a group of children in and around Lyme, Conn. The children showed signs of what initially appeared to be juvenile rheumatoid arthritis. Investigators were alerted to the unusually large numbers of these cases centering on one geographical area and eventually traced the signs and symptoms to their bacterial origins. The condition was named Lyme disease.

In 2002, approximately 23,000 cases of Lyme disease were reported to the Centers for Disease Control and Prevention (CDC). According to the CDC, the disease is greatly underreported. The U.S. Department of Health and Human Services says that the number of reported cases of Lyme disease and the number of geographic areas in which they occur is increasing. This may be due to the recent increase in the Northeastern deer population, which carry the ticks, and the increase in housing developments in rural areas. Most cases occur in the Northeastern, mid-Atlantic and upper Midwestern states and along the northern Pacific coast of California.

Lyme disease can affect people of all ages. It's most commonly characterized by a distinctive rash, flu-like symptoms and aching joints. To contract Lyme disease, you have to be bitten by an infected deer tick. Not all deer ticks in a high-risk area are infected with the bacterium that causes Lyme disease. And only a small percentage of people who are bitten by a deer tick get Lyme disease. Still, take proper precautions in areas where ticks live. Increased awareness and prevention are key to avoiding Lyme disease.