Dear Doctor: I've been reading a lot lately about something called RSV, which acts like a cold but turns out to be way worse, especially in kids. What is it, and how is a parent supposed to know the difference?

Dear Reader: You're referring to respiratory syncytial virus, which is often shortened to its initials, RSV. It's both very common and quite contagious. In fact, most children will have had a case of it by age 2.

The virus, which infects the respiratory epithelium, the specialized layer of cells that line the nasal and lung passages, causes inflammation. You're correct that the initial symptoms are just like those of a cold. Often, you'll also see a noticeable drop in the child's appetite, and he or she may run a fever as well. The symptoms come on slowly, appearing in stages. Parents report that first they'll notice their child becoming increasingly fussy, and then gradually listless. As you pointed out in your question, this all lines up with the symptoms and onset of a typical cold.

The good news is that for most children, infection with RSV stays within the parameters of a bad cold. In those cases, the symptoms can be managed with over-the-counter medications like ibuprofen or acetaminophen to relieve pain and bring down the fever. During the week or two that it takes to recover from a typical bout with the virus, it's also important to make sure the child stays hydrated.

But for some babies, particularly those younger than 6 months old, and those born prematurely, the virus can be life-threatening. Also at heightened risk are babies and children with Down syndrome, people with suppressed immune systems and the elderly. For that reason, it's vital to monitor RSV symptoms and act quickly if they escalate.

The danger arises from the degree of inflammation the virus causes in some individuals, as well as the increase in mucus production. Both make it increasingly difficult to breathe. RSV can also lead to pneumonia and bronchiolitis, an acute lower respiratory infection. As soon as you realize that a case of RSV has moved into dangerous territory, it's vital to see your primary care physician. Although there is no specific medication that targets the virus at this time, your doctor will know whether hospitalization is the next necessary step. In the hospital, the medical staff can initiate interventions to help with the patient's breathing and hydration, as well as provide close monitoring of the progress of the virus. In the majority of cases, hospitalization lasts only a day or two.

Up to one-third of all hospitalizations for respiratory viruses each year are due to severe cases of RSV -- approximately 57,000 children younger than 5, according to the Centers for Disease Control and Prevention. All of which makes the recent announcement from Canadian researchers that they have identified a promising antiviral compound to target RSV welcome news. It is said to be similarly effective against the mosquito-borne Zika virus, which is responsible for severe defects in the unborn children of women who become infected while pregnant. The researchers say that drug development of this antiviral is now underway.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o Media Relations, UCLA Health, 924 Westwood Blvd., Suite 350, Los Angeles, CA, 90095. Owing to the volume of mail, personal replies cannot be provided.)

Dear Doctor: I'm one of those Type A people who's pretty much always stressed-out. My wife got me to try yoga about six months ago and I'll admit, I do feel better. Now our local TV station has reported that yoga and meditation might actually be changing my genes. How can that be?

Dear Reader: First, congratulations on trying something new (we know it's not always easy) to improve your quality of life. The day that you stretched and visualized and breathed deep for the first time, you joined a growing groundswell of interest into yoga and meditation as avenues to enhanced well-being.

A nationwide survey three years ago found that between 2002 and 2015, the number of adults who regularly practice yoga doubled to 21 million. With this level of interest, it's no surprise that biological effects of yoga and meditation would become the subjects of even wider scientific inquiry. What was unexpected, though, were the results of a recent study. According to British researchers, who parsed the data from a group of previously published studies, mind–body interventions like yoga and meditation can affect the body at the cellular level.

Curious about the molecular mechanisms behind the mounting anecdotal evidence about the benefits of mind-body interventions, the researchers chose 18 studies into the effects of yoga, mindfulness meditation, Tai Chi, Qigong and deep breathing. A total of 846 people took part in those studies, each of which analyzed gene expression in their participants. That is, they looked at how each person was affected at a cellular level. What they found was that each of the mind-body interventions appeared to put the brakes on the genes and the genetic pathways that promote inflammation. Although inflammation is a crucial part of the body's immune response, it's a double-edged sword. The inflammation response protects the body from foreign invaders and after an injury. But when inflammation continues unabated, it creates problems of its own. Conditions like arthritis, asthma, diabetes, many cancers, atherosclerosis and various types of dementia all have chronic inflammation in common.

When the researchers analyzed the data in the 18 studies, it turned out that each of the mind-body interventions decreased the activity of genes and gene pathways involved in inflammation. As you say in your question, news reports have said that yoga and meditation changed peoples' genes. But they didn't. What did happen is that these activities appeared to affect how those genes behaved. And what was particularly interesting was that, despite the differences in the various techniques, the outcome -- a lessening of inflammation -- remained consistent. Seated meditation is, obviously, almost exclusively stationary. Tai Chi, yoga and Qigong, meanwhile, involve varying degrees of physical exertion. Yet all yielded similar benefits.

Whether you're actively bending and stretching and deep breathing or simply taking 20 or 30 minutes to clear your mind, the study's authors concluded, the daily practice leaves a "molecular signature" on your cells. This, in turn, can reduce and even reverse how stress and anxiety affect the body at a cellular level. Not a bad return on the investment.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o Media Relations, UCLA Health, 924 Westwood Blvd., Suite 350, Los Angeles, CA, 90095. Owing to the volume of mail, personal replies cannot be provided.)

Dear Doctor: It seems like everyone has a food allergy these days. Is it true that kids can outgrow them? Apparently, the test for this is just to eat a little bit of food and see what happens. Can you do this at home -- with an EpiPen at the ready, of course?

Dear Reader: According to the latest research, close to 4 percent of us have either an out-and-out food allergy or what is known as an intolerance, which makes consuming certain foods problematic.

That number comes from a study published last year in the Journal of Allergy and Clinical Immunology. Researchers sifted through the electronic health records of 2.7 million people, looking for allergy-related data. The analysis identified 97,482 people who had at least one food allergy or intolerance.

The study found food allergies to be more prevalent in girls and women, as well as in people of Asian descent. Shellfish was the most common allergen. This was followed, in descending order, by fruits or vegetables, dairy and peanuts. The researchers targeted adverse reactions that ranged from hives and shortness of breath to anaphylaxis, an allergic reaction so severe that it is potentially life-threatening. And while this latest research is indeed compelling, it's important to note that food allergies are often self-reported, which leaves a bit of leeway in the data.

The test you're referring to in your question is often referred to as a "food challenge." Before we go any further, we'd like to emphasize that no, this should not be done at home, EpiPen or not. Due to the potential for severe and life-threatening reactions, a food challenge should always be performed under medical supervision. The point of the test is twofold. You're looking at whether the food in question still causes an allergic reaction. And if so, how much of the food did it take for the reaction to begin?

Those of you who have taken a food challenge know that you start with a tiny amount of the substance in question, just a crumb, really. Then you wait for a period of time, 20 to 30 minutes or so, to see what the immune system thinks. If all is calm, you then try a larger amount and wait again. This continues until, if there has been no sign of an allergic response, you are able to tolerate a full-size portion of the food in question. The full test takes anywhere from four to six hours.

Between 60 and 80 percent of children who have allergies to eggs or milk will outgrow them by the time they hit their mid-teens. For nut allergies, the numbers are lower. About 20 percent of children allergic to peanuts will go on to tolerate them later in life. For tree nuts, that number drops to 14 percent. Very few children who are allergic to shellfish -- maybe 4 percent -- ever outgrow the allergy. And while some adults may find that they grow to tolerate foods to which they had previously been allergic, that turns out to be a lot less likely than in children.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o Media Relations, UCLA Health, 924 Westwood Blvd., Suite 350, Los Angeles, CA, 90095. Owing to the volume of mail, personal replies cannot be provided.)