Epstein-Barr virus (EBV), a widespread human herpes virus, can cause mononucleosis — but usually it doesn't. In fact, most EBV infections aren't noticeable, even when they're most active in your body. By age 35, almost everyone has antibodies to EBV, indicating past infection.

It takes more than an uncovered cough or sneeze to transmit EBV. During primary infection, people shed the virus in saliva. You need close contact, such as kissing or sharing a cup with an infected person, to catch EBV.

The infection generally causes no signs or symptoms, except in teenagers and young adults. In that age group, at least a quarter of infections cause mononucleosis — a disease that features fatigue, headache, fever, sore throat and swollen lymph nodes.

Most people who have infectious mononucleosis (mono) will have it only once. Rarely, however, mononucleosis symptoms may recur months or even years later.

Most cases of mononucleosis are caused by infection with the Epstein-Barr virus (EBV). Once you're infected with EBV, you carry the virus — usually in a dormant state — for the rest of your life. Periodically, however, the virus may reactivate. When this happens, the virus can be detected in your saliva — but you're not likely to become ill. Rarely, reactivated EBV may cause illness in people who have weak immune systems, such as those who have AIDS.

Mononucleosis rarely leads to a serious condition called chronic active EBV infection, which is characterized by persistent symptoms and a viral infection that lasts longer than usual after the initial mononucleosis diagnosis.

If you're experiencing signs or symptoms of mononucleosis — such as fatigue, weakness, fever, sore throat and swollen lymph nodes — and you've had mono before, consult your doctor to determine the cause of your current symptoms. Keep in mind that many other conditions, such as hepatitis and toxoplasmosis, can mimic the symptoms of mononucleosis.

Monosodium glutamate (MSG) is a flavor enhancer commonly added to Chinese food, canned vegetables, soups and processed meats. The Food and Drug Administration (FDA) has classified MSG as a food ingredient that's "generally recognized as safe," but its use remains controversial. For this reason, when MSG is added to food, the FDA requires that it be listed on the label.

MSG has been used as a food additive for decades. Over the years, the FDA has received many anecdotal reports of adverse reactions to foods containing MSG. These reactions — known as MSG symptom complex — include:

• Headache
• Flushing
• Sweating
• Facial pressure or tightness
• Numbness, tingling or burning in the face, neck and other areas
• Rapid, fluttering heartbeats (heart palpitations)
• Chest pain
• Nausea
• Weakness

However, researchers have found no definitive evidence of a link between MSG and these symptoms. Researchers acknowledge, though, that a small percentage of people may have short-term reactions to MSG. Symptoms are usually mild and don't require treatment. The only way to prevent a reaction is to avoid foods containing MSG.

It depends on the type of magnetic resonance imaging (MRI) scan you're scheduled to have — an MRI with contrast or an MRI without contrast. There are no special concerns for people with kidney problems having an MRI without contrast.

Contrast agents, including gadolinium (gad-oh-LIN-e-um), are used to enhance some MRI scans. Contrast agents are injected into a vein in your hand or arm.

Gadolinium-containing contrast agents may increase the risk of a rare but serious disease called nephrogenic systemic fibrosis in people with severe kidney failure. Nephrogenic systemic fibrosis triggers thickening of the skin, organs and other tissues.

Before you have an MRI, make sure your doctor knows about your kidney problems. Blood tests can reveal how severely your kidney function is impaired, which can help determine your risk of nephrogenic systemic fibrosis.

If your doctor still recommends an MRI with gadolinium despite the potential risks, you may be given the lowest possible dose of the form of gadolinium that's been associated with the fewest complications.

Your doctor also may recommend hemodialysis — a procedure that filters wastes from your blood via a machine — immediately after the MRI.

That's not an easy question to answer because there's not a lot of research on the long-term effects of the dietary supplement called methylsulfonylmethane (MSM). MSM is formed using dimethyl sulfoxide (DMSO), an organic form of sulfur that's also used as a dietary supplement.

Animals observed for 90 days on a daily dose of MSM five to seven times greater than what's typically used in people had no serious problems. Stomach upset, diarrhea and headache have been reported in human trials of MSM lasting up to 12 weeks. However, people taking a placebo also reported similar symptoms.

Since little is known about the long-term safety of MSM, it's no surprise that the efficacy also is unclear. Some studies have shown slight improvements in arthritis symptoms, but these studies were small and short term, so no definitive conclusions can be made.

Although there is great interest in using MSM to treat a variety of conditions, including arthritis, more research is needed to determine its benefits and risks.

A small amount of mucus in stool is usually nothing to worry about. Stool normally contains a small amount of mucus — a jellylike substance that your intestines make to keep the lining of your colon moist and lubricated.

But you should talk to your doctor if you notice an increased amount of mucus in stool — particularly if it begins happening regularly or if it's accompanied by bleeding or a change in bowel habits.

Larger amounts of mucus in stool, associated with diarrhea, may be caused by certain intestinal infections. Bloody mucus in stool, or mucus accompanied by abdominal pain, can represent more serious conditions — Crohn's disease, ulcerative colitis and even cancer.

Monounsaturated fatty acids (MUFAs) are a healthy type of fat. Replacing less healthy fats, such as saturated fats and trans fats, with unsaturated fats, such as MUFAs and polyunsaturated fats, may offer health benefits.

Consuming monounsaturated fatty acids may help lower your risk of heart disease by improving your risk factors. For instance, MUFAs may lower your total and low-density lipoprotein (LDL) cholesterol levels but maintain your high-density lipoprotein (HDL) cholesterol level.

MUFAs may also help improve the function of your blood vessels. And some research shows that MUFAs may also benefit insulin levels and blood sugar control, which can be especially helpful if you have type 2 diabetes.

MUFAs are a central part of the heart-healthy Mediterranean diet. MUFA-rich foods in your diet include:

• Olive oil
• Nuts, such as almonds, cashews, pecans and macadamias
• Canola oil
• Avocados
• Nut butters
• Olives
• Peanut oil

But don't go overboard. All fats, including MUFAs, are high in calories, so use MUFAs only in moderation. Consume MUFA-rich foods instead of other fatty foods, not in addition to them.

"Multigrain" and "whole grain" are not interchangeable terms. Whole grain means that all parts of the grain kernel — the bran, germ and endosperm — are used. In contrast, multigrain means that a food contains more than one type of grain, although none of them may necessarily be whole grains. The same goes for other variations, such as the term "seven grain."

Whole-grain foods are a healthy choice because they contain nutrients, fiber and other healthy plant compounds found naturally in the grain. Look for products that list the first ingredient as "whole wheat," "whole oats" or a similar whole grain.

While "whole grains" may signify one of many types of healthy grains, "whole wheat" labels the specific grain used. Either term may identify a food that's a good source of fiber, several B vitamins and minerals.

Healthy adults should eat at least three 1-ounce (28-gram) equivalents of whole grains a day as part of a balanced diet.

Epileptic seizures are more common in people who have multiple sclerosis (MS) than in those who don't have MS. While it's estimated that less than 3 percent of people without MS have seizures, about 2 to 5 percent of people with MS are thought to have active seizures.

Exactly why these seizures occur more often in people with MS isn't completely understood. MS lesions in certain areas of the brain might trigger these seizures. However, lesions are very common in MS, and seizures are unusual, so there are probably other factors that play a role in seizures, too.

Seizures may be the first noticeable sign of MS before diagnosis. Seizures can also occur during times when MS symptoms flare up. In some cases, seizures might be the only sign of an MS flare. But, the majority of seizures occur unrelated to MS relapses, and the occurrence of a seizure soon before diagnosis of MS may just be a chance occurrence.

Most seizures can be controlled with anti-seizure medication.

Multivitamins aren't necessary for most healthy children who are growing normally.

Foods are the best source of nutrients. Regular meals and snacks can provide all the nutrients most preschoolers need.

While many young children are picky eaters, that doesn't necessarily mean that they have nutritional deficiencies. Many common foods — including breakfast cereal, milk and orange juice — are fortified with important nutrients, such as B vitamins, vitamin D, calcium and iron. So your child may be getting more vitamins and minerals than you think.

Furthermore, multivitamins aren't without some risks. Megadoses of vitamins and minerals can be toxic. In addition, some vitamins and minerals can interact with medications your child may take.

Talk with your child's doctor if you're concerned about whether your child is getting the recommended level of vitamins and minerals. A multivitamin might be helpful for your child if he or she:

• Has a delay in physical and developmental growth (failure to thrive)
• Has certain chronic diseases or food allergies
• Has a restrictive diet, such as a strict vegan diet

If your child's doctor recommends a multivitamin, choose one that is designed for your child's age group and doesn't provide more than 100 percent of the Daily Value of vitamins and minerals. In addition, keep multivitamins out of your child's reach and make it clear that they aren't candy.