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Gastritis isn't one disease but a group of conditions, all of which are characterized by inflammation of the lining of your stomach. Commonly, the inflammation results from infection with the same bacterium that causes most stomach ulcers. Yet other factors — including traumatic injury and regular use of certain pain relievers — also can contribute to gastritis.

In spite of the many conditions associated with gastritis, the signs and symptoms of the disease are very similar: A burning pain in your upper abdomen and occasionally, bloating, belching, nausea or vomiting.

In some cases, gastritis can lead to ulcers and an increased risk of stomach cancer. For most people, however, gastritis isn't serious and improves quickly with treatment.

The signs and symptoms of gastritis, which are often relatively mild and short-lived, include:

• A gnawing or burning ache or pain (indigestion) in your upper abdomen that may become either worse or better when you eat
• Nausea
• Vomiting
• Loss of appetite
• Belching or bloating
• A feeling of fullness in your upper abdomen after eating
• Weight loss

Gastritis that occurs suddenly (acute gastritis) usually results in the classic combination of nausea and burning pain or discomfort in your upper abdomen, whereas chronic gastritis, which develops gradually, is more likely to cause a dull pain and a feeling of fullness or loss of appetite after a few bites of food. For many people, though, chronic gastritis causes no problems at all.

Occasionally, gastritis may cause stomach bleeding, but it's rarely severe unless there's also ulceration of your stomach lining. Bleeding in your stomach can cause you to vomit blood or pass black, tarry stools and may require immediate medical care.

Because gastritis is one of many common digestive problems with similar signs and symptoms, it's easy to confuse with other conditions, including:

• Gastroenteritis. Also called stomach flu, gastroenteritis usually results from a viral infection of your intestines. Signs and symptoms include diarrhea, abdominal cramps, and nausea or vomiting, as well as indigestion. Symptoms of gastroenteritis often resolve within a day or two, whereas the discomfort of gastritis may be ongoing.
• Heartburn. This painful, burning sensation behind your breastbone usually occurs after a meal. It develops when stomach acid backs up into your esophagus, the tube that connects your throat to your stomach. Heartburn can also lead to a sour taste and the sensation of partially digested food re-entering your mouth.
• Stomach ulcers. If a gnawing or burning pain in your stomach is persistent and severe, you may have an ulcer. Stomach (peptic) ulcers are open sores that develop on the inside lining of the stomach. The most prominent symptom is pain, which is frequently worse at night or when your stomach is empty. Gastritis and stomach ulcers share some of the same causes — especially H. pylori infection — and the one may be a precursor to the other.
• Nonulcer dyspepsia. Commonly referred to as indigestion, nonulcer dyspepsia is a functional disorder and not necessarily related to a particular disease. The exact cause isn't known, but stress and overindulging in fried, spicy or fatty foods can aggravate or trigger the upper abdominal pain, bloating, belching and nausea that characterize the condition.

Your stomach — a hollow, muscular sac — sits in the upper left corner of your abdomen, just under your rib cage. The typical adult stomach is around 10 inches long and can expand to hold about 1 gallon of food and liquid. When your stomach is empty, its tissues fold in on themselves, a bit like a closed accordion. As your stomach fills and expands, the folds gradually disappear.

Your stomach processes and stores food, which it gradually releases into your small intestine. When food arrives from your esophagus, a muscular ring at the joining of your esophagus and stomach (lower esophageal sphincter) relaxes to let it in. Your stomach walls, lined with layers of powerful muscles, then begin churning the food, mixing it into smaller and smaller pieces. At the same time, glands in the wall of your stomach pump out gastric juices — including enzymes and stomach acids — that help break food down further.

One of these, hydrochloric acid, is so caustic that it can dissolve iron nails. Your stomach's tissues are protected from this corrosive acid by the mucous-bicarbonate barrier — a layered buffering system in which bicarbonate regulates the stomach's acid-alkaline balance, and mucous provides a thick, sticky coating for the stomach walls.

Possible causes numerous
Gastritis usually develops when these and other protective mechanisms are overwhelmed, damaging and inflaming your stomach lining. Some of the many factors that can contribute to or trigger gastritis include:

• Bacterial infection. A majority of the world's population is infected with corkscrew-shaped bacteria called Helicobacter pylori (H. pylori) that live deep in the mucous layer that coats the lining of your stomach. Although it's not entirely clear how the bacteria are transmitted, it's likely they spread from person to person through the oral-fecal route or are ingested in contaminated food or water. H. pylori infection frequently occurs in childhood and can last throughout life if not treated. It's now known to be the primary cause of stomach ulcers and is a leading cause of gastritis. Long-term infection with the bacteria causes a widespread inflammatory response that leads to changes in the stomach lining. One of these changes is atrophic gastritis, a condition in which the acid-producing glands are slowly destroyed. Scientists speculate that the resulting low acid levels may prevent cancer-causing toxins from being properly broken down or flushed out of your stomach, increasing your risk of stomach cancer. Yet most people with chronic H. pylori infection don't develop cancer, and many have no symptoms of gastritis, indicating that other factors may make some people more vulnerable to the bacteria.
• Regular use of pain relievers. Nonsteroidal anti-inflammatory drugs (NSAIDs) such as aspirin, ibuprofen (Advil, Motrin, others), and naproxen (Aleve) can cause stomach inflammation by reducing a substance that preserves the protective stomach lining (prostaglandin). Stomach problems are less likely to develop if you take NSAIDs only occasionally, but regular use or overuse is a common cause of both gastritis and stomach ulcers.
• Excessive alcohol use. Alcohol can irritate and erode the mucous lining of your stomach, making the tissue more vulnerable to the caustic effects of normal stomach secretions.
• Cocaine use. Cocaine can damage your stomach, leading to bleeding and gastritis.
• Stress. Severe stress due to major surgery, traumatic injury, burns or severe infections can cause gastritis as well as ulcers and stomach bleeding.
• Autoimmune disorder. Autoimmune atrophic gastritis develops when your immune system attacks healthy cells in your stomach lining. This triggers an inflammatory response that gradually thins the lining, destroys acid-producing glands and interferes with the production of intrinsic factor, a substance that helps your body absorb vitamin B-12. Lack of B-12, in turn, can lead to pernicious anemia, a serious condition that if not treated can affect nearly every body system. Autoimmune atrophic gastritis is particularly common in older adults.
• Crohn's disease. Although this bowel disease usually causes chronic inflammation of the lining of the digestive tract, it can sometimes inflame the stomach lining as well. Even when your stomach is affected, however, the signs and symptoms of Crohn's disease — abdominal pain and watery diarrhea — are more prominent than symptoms of gastritis are.
• Radiation and chemotherapy. Cancer treatments such as chemotherapy and radiation can inflame your stomach lining, leading to both gastritis and stomach ulcers. When you're exposed to small amounts of radiation, the damage is often temporary, but large doses usually cause irreversible erosion of the stomach lining and destruction of acid-producing glands.
• Bile reflux disease. Bile — a fluid that helps you digest fats — is produced in your liver and stored in your gallbladder. When it's released from the gallbladder, bile travels to your small intestine through a series of thin tubes. Normally, a ring-like sphincter muscle (pyloric valve) prevents bile from flowing back into your stomach from your small intestine. But if this valve doesn't work properly, bile can back up into your stomach, leading to inflammation and gastritis.
• Other factors. Gastritis may be associated with other medical conditions, including HIV/AIDS, parasitic infections, some connective tissue disorders, and liver or kidney failure.

The most significant risk factor for gastritis is infection with H. pylori bacteria. In the United States, one in five people younger than 40 and half of people older than 60 are infected. The numbers are much greater in developing nations.

Other factors that may put you at increased risk of gastritis include:

• Regular use of aspirin or other NSAIDs. If you regularly take aspirin to prevent a heart attack or stroke, you're at risk of developing gastritis. The same is true if you take anti-inflammatory pain relievers for arthritis or another chronic condition. That's because long-term use of aspirin and other NSAIDs can cause stomach irritation and bleeding.
• Race. In the United States, blacks, Indians and Hispanics are more likely to have gastritis associated with H. pylori infection than are people of other races. Autoimmune gastritis, on the other hand, is more common among blacks and people of Northern European descent.
• Age. Adults age 60 and older are at increased risk of gastritis because the stomach lining tends to thin with age and because older adults are more likely to have H. pylori infection or autoimmune disorders than younger people are.

Nearly everyone has experienced a bout of indigestion and stomach irritation. Most cases of indigestion are short-lived and don't require medical care. But if you experience signs and symptoms of gastritis consistently for a week or longer, see your doctor. And be sure to tell your doctor if you experience stomach problems after taking any prescription or over-the-counter drug, especially aspirin or other pain relievers.

If you are vomiting blood or have blood in your stools, see your doctor right away to determine the cause.

Although your doctor is likely to suspect gastritis after talking to you about your medical history and performing a thorough exam, you may also have certain tests to pinpoint the exact cause. These tests include:

• Blood tests. Your doctor may order a blood test to check for the presence of H. pylori antibodies. A positive test shows that you've come in contact with the bacteria at some time in your life, but it doesn't necessarily indicate current infection. Blood tests can also check for anemia, which may result from stomach bleeding associated with gastritis.
• Breath test for H. pylori infection. This simple test can help determine whether you are currently infected with H. pylori bacteria.
• Stool tests. This test checks for H. pylori in a sample of your stool. A positive test suggests current infection. Your doctor may also test for the presence of blood in your stool, a sign of stomach bleeding that can accompany gastritis and stomach ulcers.
• Upper gastrointestinal endoscopy. This procedure allows your doctor to see abnormalities in your upper gastrointestinal (GI) tract that may not be visible on X-rays. For the test, your doctor inserts a thin, flexible, lighted tube (endoscope) through your mouth and into your esophagus, stomach and the first part of your small intestine. Your throat is usually numbed before you're asked to swallow the endoscope, and you'll receive additional medication to ensure that you're comfortable during the procedure. If any tissue in your upper intestinal tract looks suspicious, your doctor can remove a small sample (biopsy) using instruments inserted through the endoscope. The sample is then sent to a lab for examination by a pathologist. Upper endoscopy takes about 20 to 30 minutes, although you won't be sent home until the medication wears off — usually one to two hours later. Risks of the procedure are rare and include bleeding and perforation of the stomach lining. The most common complication is a slight sore throat from swallowing the endoscope.
• Upper gastrointestinal X-ray. These X-rays of your stomach and small intestine check for signs of gastritis and other digestive problems. They're often taken after you swallow a liquid (barium) that coats the lining of your digestive tract, making it show up more clearly on the X-rays.

Left untreated, gastritis may lead to stomach ulcers and stomach bleeding. And some forms of chronic gastritis may increase your risk of stomach cancer, especially if you have extensive thinning of the stomach lining and changes in the lining cells.

Most stomach cancers are adenocarcinomas, which start in the glandular cells in the mucosa, the stomach's innermost lining. Type 1 adenocarcinomas, in particular, usually result from H. pylori infection. Another, much less common cancer that's also associated with H. pylori infection, is a slow-growing cancer of immune system tissue in the stomach wall. Known medically as mucosa-associated lymphoid tissue (MALT) lymphomas, these tumors are often curable when found in the early stages.

Treatment of gastritis depends on the specific cause and may include lifestyle changes, medications or, in rare cases, surgery to treat an underlying disease or condition.

Medications to treat stomach acid
Stomach acid irritates inflamed tissue in your stomach, causing pain and further inflammation. That's why, for most types of gastritis, treatment involves taking drugs to reduce or neutralize stomach acid, such as:

• Antacids. Over-the-counter antacids (Maalox, Mylanta, others) in liquid or tablet form are a common treatment for mild gastritis. Antacids neutralize stomach acid and can provide fast pain relief.
• Acid blockers. When antacids don't provide enough relief, your doctor may recommend a medication such as cimetidine (Tagamet), ranitidine (Zantac), nizatidine (Axid) or famotidine (Pepcid) that helps reduce the amount of acid your stomach produces.
• Proton pump inhibitors. An even more effective way to reduce stomach acid is to shut down the acid "pumps" within acid-secreting stomach cells. Proton pump inhibitors reduce acid by blocking the action of these tiny pumps. This class of medications includes omeprazole (Prilosec), lansoprazole (Prevacid), rabeprazole (Aciphex) and esomeprazole (Nexium). Proton pump inhibitors also appear to inhibit H. pylori activity.
• Cytoprotective agents. These medications are designed to help protect the tissues that line your stomach and small intestine. They include the medications sucralfate (Carafate) and misoprostol (Cytotec). If you're taking NSAIDs regularly, your doctor may suggest that you also take one of these medications to protect your stomach. Another cytoprotective agent is bismuth subsalicylate (Pepto-Bismol). In addition to protecting the lining of your stomach and intestines, bismuth preparations appear to inhibit H. pylori activity.

Medications to treat H. pylori
Doctors use several regimens to treat H. Pylori infection. Most use a combination of two antibiotics and a proton pump inhibitor. Sometimes bismuth (Pepto-Bismol) also is added to the mix. The antibiotic helps destroy the bacteria, and the acid blocker or proton pump inhibitor relieves pain and nausea, heals inflammation and may increase the antibiotic's effectiveness.

H. pylori treatments aren't always completely successful — eradication rates vary widely, depending on the regimen — but three-drug combinations seem to be more effective than those containing just two drugs. Longer treatment times — two weeks as opposed to 10 days — also seem to increase effectiveness.

To ensure that H. pylori has been eliminated, your doctor may test you after treatment. The breath test and the stool test are the preferred ways to check for remaining signs of H. pylori. The blood test may remain positive for months or longer despite the fact that the bacteria have been eliminated.

Although you can't always prevent H. pylori infection, these suggestions can help reduce your risk of gastritis:

• Eat smart. If you experience frequent indigestion, eat smaller, more frequent meals to buffer stomach acid secretion. In addition, avoid any foods you find irritating, especially those that are spicy, acidic, fried or fatty.
• Limit or avoid alcohol. Excessive use of alcohol can irritate and erode the mucous lining of your stomach, causing inflammation and bleeding.
• Don't smoke. Smoking interferes with the protective lining of the stomach, making your stomach more susceptible to gastritis as well as ulcers. Smoking also increases stomach acid, delays stomach healing and is a leading risk factor for stomach cancer. Still, quitting isn't easy, especially if you've smoked for years. Talk to your doctor about methods that may help you stop smoking.
• Switch pain relievers. If possible, avoid taking NSAIDs — aspirin, ibuprofen and naproxen. These over-the-counter medications can cause stomach inflammation or make existing irritation worse. Instead, switch to pain relievers containing acetaminophen.
• Follow your doctor's recommendations. Your doctor may recommend that you take an over-the-counter antacid or acid blocker to help prevent recurring gastritis.

Digestive problems ranging from simple stomach upset to stomach cancer can occur for many reasons, including lifestyle choices you can control. In general, to keep your digestive system healthy, doctors recommend that you:

• Practice good eating habits. Just as important as what you eat is the manner in which you eat. Eat moderate proportions, eat at regular times and relax while you eat.
• Maintain a healthy weight. Digestive problems can occur no matter what your weight. But heartburn, bloating and constipation tend to be more common in people who are overweight. Maintaining a healthy weight can often help prevent or reduce these symptoms.
• Get plenty of exercise. Aerobic exercise that increases your breathing and heart rate also stimulates the activity of intestinal muscles, helping to move food waste through your intestines more quickly. It's best to aim for at least 30 minutes of aerobic activity every day.
• Manage stress. Stress increases your risk of heart attack and stroke, dampens your immune system and can trigger or aggravate skin problems. It also increases stomach acid production and slows digestion. Because stress is unavoidable for most people, the key is to learn to handle it effectively — a task that's made easier by a nutritious diet, adequate rest, regular exercise and healthy ways to relax. If you have trouble relaxing, consider taking up meditation or studying yoga or tai chi. These disciplines can help focus your mind, calm your anxieties and reduce physical tension. Therapeutic massage may also loosen taut muscles and calm frazzled nerves.