Dear Doctor: We live near a freeway with a lot of traffic. Do I need to be worried about my kids developing asthma?

Dear Reader: This is a valid question. Cars release a number of small particles into the air that can irritate the lungs. This particulate matter, in addition to nitric oxide and black carbon, has been associated with asthma. Children are more vulnerable to the effects of pollution because their lungs and immune system are still developing.

An analysis of many studies, published in the journal Allergy, found a significant association between traffic-related air pollution and asthma. The association was seen as early as the age of 1 and increased as the child became older. The rise in asthma as kids get older seems to be related both to structural changes that pollution creates in the lungs and also to the extent of time that older children spend outside compared to younger children.

One other important aspect of asthma is that it can be exacerbated by stress. Noise pollution and the danger of cars in close proximity may worsen asthma symptoms in children because they can create a more stressful environment. This is an important factor if your child already has asthma.

A recent study in Minnesota evaluated the number of asthma cases in the emergency room, in the hospital and in a clinical setting. The researchers then looked at the proximity of people to a major source of traffic. After taking poverty out of the equation, which is in itself a risk factor for asthma, the researchers found that, as traffic density increased, so did the number of asthma exacerbations, or worsening of asthma symptoms. In this study, for every 10 percent increase in traffic density, there was a 15 percent increase in asthma-related visits to the emergency room, hospital or outpatient clinic.

Clearly, if you have a child with asthma, moving him or her away from traffic would indeed reduce the chance of a severe asthma attack.

I understand your concern. It is also a societal concern. Despite the evidence linking pollution to asthma, the levels of pollutants that are associated with an increased risk of asthma are well below the guidelines from the World Health Organization.

This doesn't mean that if you live near a freeway, you have to move. The majority of children who live near a freeway do not get asthma. But if your child is already showing signs of asthma at a young age, then moving to an area with fewer pollutants is perhaps something you should consider, if it is at all possible.

It took many years for our society to accept the ills of secondhand smoke from cigarettes. When it did, smoking was then banned from many public places, even casinos. It is more difficult to ban housing near freeways or heavily trafficked areas, especially when that housing already exists.

(Robert Ashley, M.D., is an internist and assistant professor of medicine at the University of California, Los Angeles.)

(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.)

Dear Doctor: We're finally winning the battle against sugary soft drinks in our home, but a family friend insists that the sparkling water our kids are drinking instead is bad for their bones and teeth. Is this really true?

Dear Reader: First, congratulations on weaning your family off of soft drinks. One out of every three Americans drinks at least one (and often more) sugar-packed soda or other sweetened beverage every day. This puts them at increased risk for serious health problems such as obesity, Type-2 diabetes and even heart disease.

Although in a perfect world we would all stick to plain water to get the hydration we need, the truth is that can get boring. It's no surprise, then, that sparkling water, with its fizzy bubbles and wide range of flavors, has become a go-to replacement for people who want to cut back on calorie-laden sodas.

Sparkling water, which typically has no calories, is made when carbon dioxide gas is dissolved in plain water, a process known as carbonation. This results not only in the bubbles we love, but also creates carbonic acid, which gives fizzy water a mildly tart flavor. (We'll get back to that in a minute.)

The concern voiced by your family friend, that drinking carbonated water weakens bones, quite possibly finds its roots in a study conducted in 2006. Known as the Framingham Osteoporosis Study, researchers tied the consumption of cola beverages to decreased density in the hip bones of older women.

But the operative word here turns out to be "cola." Women in the study who drank non-cola beverages did not exhibit increased bone loss. The researchers concluded that carbonation doesn't damage your bones.

As to the question of carbonation being bad for your teeth, we need to talk about the carbonic acid we mentioned earlier.

While it's true that the process of carbonation results in the creation of an acid, it's a very weak one. Plain bottled water has a neutral pH of 7. Carbonated water such as Perrier is only slightly more acidic, with a pH of 5.25. According to the American Dental Association (ADA), that's "minimally corrosive." Cranberry juice, by contrast, with a pH of 2.5, is considered by the ADA to be "extremely corrosive."

So the good news is that you and your family are on the right track with fizzy waters replacing sodas and other sweet drinks. Just be sure to always read the labels. If you see the words sucrose, glucose, fructose or corn syrup, you're holding a sugary drink.

And here's a bonus for weight watchers from a National Institutes of Health study: Young women who drank a glass of fizzy water reported feeling full and satiated.

Lastly, for those of you with kids who may have heard this urban legend -- eating the carbonated candy Pop Rocks and then drinking a soda will definitely not make your stomach explode!

(Eve Glazier, M.D., MBA, is an internist and assistant professor of medicine at UCLA Health. Elizabeth Ko, M.D., is an internist and primary care physician at UCLA Health.)

(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.)

Dear Doctor: Marijuana seems to be increasingly accepted in our country. But I worry about my kids using it. Is it addictive?

Dear Reader: You're right to be worried -- and not only because marijuana can indeed be addictive.

Marijuana has gained greater acceptance in this country, not in small part because its medical use can stimulate appetite, control nausea and control pain. One potential problem with this degree of acceptance is how adolescents view the drug.

In 2015, 70 percent of high school seniors viewed marijuana as not harmful, according to the National Institute on Drug Abuse's (NIDA) Monitoring the Future survey; in 1990, only 20 percent felt this way. Interestingly enough, the 2015 survey also found that 70 percent of 12th-graders disapprove of the regular use of marijuana.

Perhaps the biggest risk with marijuana is how it affects the adolescent brain. The endocannabinoid system, a vast system of receptors within the brain, spinal cord and smaller nerves, affects multiple brain and body functions. This system continues to develop in humans until the age of 21 or so.

If used frequently in adolescence, marijuana can rewire many of these nerve pathways. These changes aren't seen as much in the adult brain and, if they surface, can be easily reversed by stopping use. In adolescents, however, this rewiring of the nervous system may create addiction.

According to the NIDA, only 9 percent of people who try marijuana become addicted. However, this number increases to 16 percent among those who start using marijuana in adolescence. It increases further if marijuana is used daily in adolescence. In fact, 17 percent of admissions to publicly funded substance abuse programs are related to marijuana.

Some of my patients argue that alcohol is a much more addictive substance and can cause withdrawal symptoms that are life threatening. That is true. However, just because one substance has particularly bad effects doesn't mean another one is safe. There are problems with each.

Marijuana not only causes short-term memory loss, it also affects mental abilities for days after its use. That means a person's ability to plan, organize, solve problems and make decisions is impaired, which has significant ramifications for adolescents trying to retain information learned in school or trying to maintain good study habits.

Further, for those predisposed to schizophrenia, marijuana can induce psychosis and, in younger users, can decrease the age of schizophrenia's onset. People with a familial predisposition to schizophrenia should certainly avoid use.

However, marijuana has not been associated with depression or bipolar disorder, and while those with generalized anxiety are more likely to use marijuana, that connection may be linked more to a need to compensate than to causal effect.

I would advise high school students not to use alcohol or marijuana in adolescence, but the reality is that your child, like many others, may be exposed to these and other drugs in high school. As a parent, be sure to watch for signs of abuse or consistent use, and to note any psychological issues that could lead to frequent marijuana use.

With the greater acceptance of marijuana within our society, increased exposure and the likelihood of abuse are rising. Guide your teenager to hobbies, sports, outdoor activities or simply reading a book as a way to cope with the stressors of high school life. And, above all, keep an open line of communication.

(Robert Ashley, M.D., is an internist and assistant professor of medicine at the University of California, Los Angeles.)

(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.)