Dear Doctor: My grandson is always carrying around a little device that he smokes like a cigarette. It puffs smoke just like one, too. I’m a former smoker, and my lungs aren't in great shape, so I’m worried. What is he using? Is it safe?

Dear Reader: Your grandson is vaping, which means he’s inhaling an aerosol produced by the device you’ve seen him using. It’s that aerosol, or vapor, that gives the practice its name. As for the specific type of device he’s using, it’s difficult to say without a clearer description. It’s definitely not an e-cigarette; those look just like tobacco cigarettes, and you would have recognized it.

E-cigarettes were the vanguard of vaping devices and first made an appearance in this country in 2007. They quickly gave way to vape pens, which as the name suggests, are slim devices that resemble a ballpoint pen. Larger and bulkier in size are vape mods, which are modified (again, there’s the root of the name) vape pens. These are known for their abundant vapor production. More recent to the marketplace is the JUUL, a small vaping device that’s about the size of a USB drive.

Whatever the specific type of device (there are many), most use disposable pods or cartridges that hold a liquid, or e-liquid, typically propylene glycol or vegetable glycerin. These liquids can contain quite a few other compounds, but at this time, manufacturers are not required to divulge them.

When heated, the liquid produces the vapor that the user is inhaling and exhaling. Most e-liquids contain nicotine, along with flavorings such as strawberry, banana, chocolate or mint. The allure of those flavorings to young people has been particularly controversial, and the outcry has resulted in a number of actions at the state and federal levels to limit their availability.

In asking whether vaping is safe, you’ve touched on a roiling debate. The general consensus is that vaping is safer than smoking cigarettes. That’s because rather than the tens of thousands of compounds produced in the burning of tobacco and its additives, many of them toxic, the number of ingredients in e-liquids is limited. However, many teens and young adults who would not otherwise have taken up smoking are finding the tech and the flavors of vaping so alluring that the practice has become widespread. It is estimated 20 percent of high school students and 5 percent of middle school students have used vaping devices, more than a third of them unaware that the product contains nicotine.

The fact is that nicotine poses a real health risk to young people, whose brains and bodies are still developing. Likewise, the effect of regularly inhaling vaporized glycerin and propylene glycol is not yet known. The practice of vaping is so new that we have to wait in real time for the results of studies into the long-term effects. So far, studies have linked vaping to hypertension, increased heart attack risk, slow wound healing, lung inflammation and increased likelihood of moving on to smoking tobacco. The Food and Drug Administration states vaping is not safe for young people. We wholeheartedly agree, and would go even further to end the sentence after the word “safe.”

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10880 Wilshire Blvd., Suite 1450, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)

Hello dear readers, and welcome to our first letters column of spring. We hope you’re enjoying the lengthening days and are recovering from the jolt of losing an hour to Daylight Saving Time. Speaking of which, we received mail regarding a recent column about the negative health effects of night shift work. These include fatigue, depression, cognitive lapses and an increased risk of heart disease, diabetes and certain cancers. This arises from the disruption of the circadian rhythm, or internal clock, which regulates our biological processes. Our internal clock oversees physiological functions at the molecular level, including cell regeneration, immune response and hormone production, and research shows no amount of extra sleep can "fix" circadian misalignment.

-- A reader from Port Neches, Texas, asked about rotational shift work, which is when day shifts and night shifts are interspersed. Although he had been comfortable working a sustained night shift schedule, he was recently assigned alternating sets of day and night shifts. “Shifting back and forth between days and nights leaves me fatigued,” he writes.

The answer is that rotational shift work, whether on a daily, weekly or even monthly schedule, makes the adverse physical effects of night shift work even worse. The circadian cycle is a powerful force, and our bodies never truly make peace with living outside of its natural rhythms. Any adjustments we are able to make take place only gradually, and over time. This means with each switch to a new schedule, our bodies start from scratch to make the slow adjustment. When work schedules change too often, our bodies just can’t catch up.

-- A reader who has been treated twice for basal cell carcinoma on her nose now uses an SPF 50 sunscreen with a high zinc oxide percentage. “I apply it every day, regardless of the weather -- whether clear and sunny or cloudy and overcast,” she writes. “But my weather app frequently shows a UV index of zero or 1. Does this mean I do not need to wear sunscreen?”

Please, do keep slathering on the sunscreen. A UV Index of zero to 2 means that for the average person, danger from the sun's UV rays is low. However, for those who burn easily or have had skin cancer, a full-spectrum sunscreen of at least SPF 30 is recommended.

-- In response to a column about healthy eating, a reader asked about fresh versus frozen produce. “I buy a lot of vegetables because I want to eat better,” she wrote. “But because I’m so busy, they sometimes go bad before I can cook them. Is frozen food so much worse for me?”

In good news for your wallet, a recent study by food scientists at the University of California, Davis found no significant nutritional differences between fresh and frozen fruit and vegetables. In fact, in some cases, as with vitamin E, frozen produce actually had higher levels of the vitamin than did fresh foods.

And all too quickly, we’ve run out of room. We love hearing from you, both the good (thank you!) and the critical.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10880 Wilshire Blvd., Suite 1450, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)

Dear Doctor: I read that New York recently banned something called activated charcoal from all food and beverages. What is that, and why on Earth would anyone ever want to ingest it?

Dear Reader: The history of food fads is as long as it is strange. Back in the 11th century, after William the Conqueror successfully led the Norman conquest of England, he tried to conquer a weight problem with a liquid diet consisting mainly of alcohol. Lord Byron, the British poet and politician, was so enamored of vinegar as a curative that he made it the cornerstone of his diet and sparked a widespread fad. In the 1830s, Americans were urged to eat a bland diet anchored by graham crackers to cool their sex drives. And in the Victorian era, women downed pills that supposedly contained a tapeworm egg (they probably didn’t) so the parasite growing in their intestines would take care of any excess calories.

Now comes activated charcoal, the latest in a centurieslong preoccupation with magical thinking about food. The substance is made by heating carbon-rich materials like wood, peat or coconut shells to extremely high temperatures. The resulting charcoal is then ground up and stripped of extraneous molecules, which creates ultra-fine particles full of holes and crevices. These increase the surface area of each minute particle, which makes available thousands of potential binding sites. Thus "activated," the charcoal can now attract molecules, ions or atoms, making it a highly effective purifier. Activated charcoal is used in water filtration, and it is a go-to treatment in many cases of overdose and poisoning.

When added to food -- the coconut variety is most widely used in this instance -- activated charcoal transforms the familiar color palette of white, beige and brown to a startling dark black. From ice cream, smoothies and sauces to burger buns, beverages and pizza crust, an ever-growing range of everyday edibles is getting the activated charcoal treatment.

To be fair, much of the current rage for charcoal-infused foods arises from their visual shock value. But due to its ability to absorb impurities, activated charcoal has been assigned a wide range of health benefits, not all of them accurate. Some animal studies have suggested that activated charcoal may reduce certain damage associated with chronic kidney disease. There is evidence that it can ease intestinal gas, though the mechanism remains unclear. Claims that activated charcoal will clear the body of toxins or decrease bad breath remain unproven.

It can present some dangers as well. The same absorbent properties that make activated charcoal effective for poison control can also interfere with the absorption of medications. It can also cause constipation.

Still, it’s easy to understand how this latest food fad took hold. It’s also not surprising that it has become a target for regulation. Last spring, the Department of Health in New York City banned the use of activated charcoal in commercial food and drink. Health officials in San Francisco are also looking into addressing the trend. Advocates of activated charcoal have pledged to push back. It will be interesting to see what happens next.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10880 Wilshire Blvd., Suite 1450, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)