Dear Doctor: Would you kindly address the risks of e-cigarettes compared to regular cigarettes? I am opposed to both because of the potential for nicotine addiction and other health issues. Some of my adult relatives, however, are convinced e-cigs are not harmful, even though they clearly seem addicted.

Dear Reader: On the surface, e-cigarettes appear to be a good idea. After all, they contain no combustible substances to become residue and enter the lungs. Instead, the devices feature a cartridge filled with a nicotine liquid that is vaporized and inhaled. Nicotine concentrations vary in the cartridges from 6 to 24 milligrams per milliliter. E-cigarettes also contain propylene glycol, which is used to prevent the liquid from evaporating, and flavorings that make the vapor more palatable.

As for their safety, first, let's assess the risk from nicotine. It's true that nicotine raises the pulse rate and increases the workload of the heart, but while smoking cigarettes is a significant risk factor for coronary artery disease and heart attacks, nicotine does not appear to be the culprit. In fact, studies have shown that people who use nicotine replacements in the form of gum, lozenges or patches have no change in their risk of heart attacks. Note, however, that rates of nicotine toxicity have substantially increased since the introduction of e-cigarettes. This occurs when someone uses too much nicotine or when someone, such as a child, ingests the liquid in one of the vials.

Second, let's assess what we don't know: the long-term effects of inhaling e-cig vapor. Acute exposure to the vapor does lead to a small increase in lung flow resistance, and the vapor could lead to more inflammation of the airways. Surveys of students in Hong Kong and in the United States have shown an increased rate of chronic cough and bronchitis among those using e-cigarettes. The vapor itself does have trace amounts of carcinogenic compounds, but at much lower levels than in combustible cigarettes.

Because the risk for lung cancer would appear to be smaller for e-cigs than for traditional cigarettes, they definitely have the edge in that respect. Additionally, e-cigarettes, like nicotine gums and patches, can decrease the desire to smoke combustible cigarettes. Studies of people using e-cigarettes to stop smoking have found rates of smoking cessation of 7.3 to 12.5 percent. And even if e-cigarettes don't actually help people stop smoking, they could theoretically decrease the number of regular cigarettes consumed. So, for those who smoke cigarettes already, e-cigarettes could provide a health benefit.

The bigger problem lies in e-cigarettes' risk to young people. Studies have shown that adolescents and young adults who use e-cigs have three times the risk of initiating regular cigarette smoking than those who don't use e-cigs. This may be due to the nicotine, of course, but regardless, it points to the potential connection between e-cigs and a lifelong nicotine addiction, with e-cigs being a gateway. Because of this potential, many doctors and anti-smoking activists have advocated banning advertisements geared toward adolescents.

In summary, perhaps the harm to your adult relatives depends on their smoking status and age. In any case, allow me to reiterate: While e-cigs seem healthier than traditional cigarettes, the long-term health effects are not known.

(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 Readers: With this year's flu season on a pace to be the worst in almost a decade, we want to take a moment to share an important letter that we received from a reader. As of this writing, at least 37 children have died from influenza infection. Because of the time lag in identifying and reporting flu deaths, officials suspect the true number is significantly higher.

Medical centers throughout the United States have admitted close to 12,000 people with confirmed cases of the flu, in many instances overwhelming the facilities. Here in California, some hospitals have resorted to setting up "surge tents" to house the crush of flu patients. Nurses and other medical personnel are being flown in from surrounding areas to help. And the capper is that, driven by H3N2, a particularly nasty strain of the influenza A virus, scientists at the Centers for Disease Control and Prevention warn that things will probably get worse.

Which brings us to the letter -- it's a plea, really -- from one of our readers. She begins by sharing that, in the five years after her diagnosis of rheumatoid arthritis, she has managed to find a treatment regimen that helps her live with this difficult disease. However, this includes medications that make her particularly vulnerable to infection. We'll let her take it from here:

"The same medications that keep my disease under control also suppress my immune system and leave me vulnerable to catching colds and other viruses that my body is unable to fight off," she writes. "As a result, I am very careful about being around other people in public places or in crowds. My request is that you please let others know that if you are not feeling well or are sick to please stay home! Those with compromised immune systems cannot fight off illness the way that you can. This has been a bad year for the flu, but it can be deadly to someone like me."

Research shows you're capable of spreading the influenza virus a day or so before you realize that you're sick. You'll continue to be capable of spreading the virus for another five to seven days. For children, it can be even longer. So the minute you recognize the onset of your own flu symptoms, whether it is fever, chest congestion or body aches, know that you're contagious. Always cover your mouth when you cough. Sneeze into a tissue. Wash your hands. Stay at home.

We have long understood that flu is transmitted via the fine mist of aerosolized droplets from a sick person's cough or sneeze. Now a new study, funded by the CDC, suggests the virus is passed along on an infected person's breath, whether or not they cough or sneeze. People are particularly infectious early in their illness, yet another argument for staying home.

The advice for staying healthy has long been frequent hand-washing, keeping surfaces clean and steering clear of individuals who are ill. While this all still holds true, researchers in the study say staying away from enclosed public spaces is equally important.

And, we would add, get your flu shot. This year's version isn't as robust as one would have wished, but it does offer a measure of protection.

(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: Could you comment on the marijuana study done in early 2016 at the University of Exeter and University College London? I'm worried about the 14-year-olds with whom I work and their dangers of psychosis. I was hoping we might start a dialogue about the risky business of marijuana.

Dear Reader: One of the big concerns about marijuana use, especially among adolescents and young adults, is the connection to psychotic episodes and lifelong schizophrenia. In people with a family history of schizophrenia, marijuana can increase the risk of such episodes and decrease the age of schizophrenia onset. The study to which you refer sheds some light on that risk.

That study focused on the AKT1 gene, which has been proposed as a possible genetic connection to this response to marijuana. The gene produces the enzyme serine-threonine protein kinase, necessary for many cellular processes throughout the body -- including the transmission of dopamine, which carries signals between brain cells. This function is known as dopamine signaling, and proper signaling is necessary for the brain responses controlling behavior and emotion.

As background, studies in mice have shown that marijuana activates the AKT1 gene in the brain's cerebellum, hippocampus and striatum. Second, schizophrenia has been linked to disturbed and hyperactive dopamine signaling. The concern is that, if AKT1 is stimulated by marijuana -- increasing dopamine transmission in the brain -- then psychosis may occur.

Note, however, that the AKT1 gene differs in people. In schizophrenia, the AKT1 2494732 type is the one most likely to be stimulated by marijuana. People with two copies of this gene type have twice the likelihood of a psychotic episode and other symptoms of schizophrenia.

The study you mention looked at 422 people, ages 16 to 23, who used marijuana at least once a month. Participants were given a pair of psychological tests at two different times: once without the use of marijuana and once with use. One psychological test was designed to detect psychotic symptoms; the other test was designed to detect dissociative and imaginative states, also called schizotypal symptoms, similar to those seen in schizophrenia. The researchers also did genotype testing to identify people with the AKT1 2494732 type.

Of the 422 participants, 197 had one copy of the gene and 91 had two copies. When intoxicated with marijuana, people with one or two copies of the AKT1 2494732 type had moderately greater psychotic symptoms, but other participants were not free of symptoms. Also, interestingly enough, schizotypal symptoms were not associated with this gene type, but were associated with a dependency to marijuana. People who were both dependent on marijuana and who had the AKT1 genotype were more likely to have psychotic symptoms.

Overall, the study does point to a genetic link between psychotic symptoms and marijuana use, but the link is more complicated than the presence of a specific genotype. Because 288 of the 422 participants had at least one copy of the gene, the data should have been more overwhelming. Clearly something else is occurring to push some people toward schizophrenia; we just don't know what.

With more definitive research, individuals could be genetically tested as to their susceptibility to schizophrenia with the use of marijuana. For now, we simply know that a family history of schizophrenia increases the risk among people who use marijuana -- making it risky business indeed.

(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.)