Dear Doctor: I've been having chest pain, and my doctor said that although I shouldn't panic, I should consider a stent. Now I read they're useless. What are my options?

Dear Reader: What you're describing is angina -- chest pain caused by decreased blood flow to the heart via the coronary arteries. Stable angina occurs with exertion, not rest, because the exertion makes your heart work harder. Unstable angina is irregular, can occur even at rest and is a harbinger of an imminent heart attack.

In 1977, doctors began to treat angina with angioplasty, which uses a balloon to open the partially clogged coronary arteries. In the 1990s, they started using stents to keep the arteries open and make them less likely to collapse. In this procedure, a metal stent is placed over a balloon so that when the balloon expands, the stent presses outward to buttress open the artery. Because these metal stents can increase the risk of blood clots, they're often now coated with a drug that prevents clots. Angioplasty has been found to reduce the risk of heart attacks and strokes in people with unstable angina.

For stable angina, the picture recently became murkier. The study to which you're referring assessed outcomes in stable angina patients with one or more coronary arteries at least 70 percent narrowed. People were excluded from the study if they'd had a previous heart attack, bypass surgery or another vessel blocked more than 50 percent but not causing symptoms. In the first six weeks of the study, participants received standard medical therapy, including blood thinners, cholesterol-lowering medication, blood pressure medications and long-acting nitrates.

After that, study subjects were randomized into a group that received a stent or a control group that didn't receive a stent. In fact, in the second group, the patients didn't even know if they'd received a stent or not. After another six weeks, all the patients underwent a cardiac stress test and an assessment of symptoms.

No difference in symptoms was found. Even an evaluation of the ability to walk on a treadmill showed no difference between the two groups. However, when given a medication to stress the heart, the stent group showed an improvement in contraction of the heart muscle as seen on ultrasound.

Similarly, a 2007 study showed no difference in death rate or heart attack rate among people with stable angina treated with angioplasty compared to those who received medical therapy. The group that received an angioplasty did report an improvement in symptoms 2 1/2 to seven years after the treatment, but it's possible the placebo effect played a role. That's because, unlike the more recent group, the 2007 study participants knew whether they'd had angioplasty.

That said, stents are not useless. They do prevent heart attacks and death in people with unstable angina, and they may benefit people with stable angina who have symptoms even on medication or who are intolerant to medication. But it seems to me that the robust benefit of stents in people with stable angina is not evident. I'd recommend talking with your doctor further; you do have a choice.

(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.)

Hello again, dear readers! Your letters continue to pour in, and we are impressed by and grateful for your curiosity, kindness and your thirst for knowledge. We, too, are lifelong students and love learning from you.

-- Lawrence, a nurse anesthetist from Suffolk, Virginia, expands on the column about bringing a written list of questions to your medical appointments. He suggests maintaining a comprehensive health profile on your computer, which can easily be printed out as needed.

"I include not only medications, but a list of diagnoses, surgical history, contact info and insurance info," Lawrence writes. "The profile is about 2 inches wide by 6 inches long and fits in the front of my wallet, where it would be easily found if I were incapacitated."

-- In response to the column about Grover's disease, a condition that manifests as a rash that can often be maddeningly itchy, readers shared novel ways to deal with the itch.

A reader diagnosed with Grover's disease five years ago recommends using a thin layer of a mentholated topical ointment, like Vicks VapoRub.

"This does two things for me," he writes. "First and fabulous, the itching pain ceases immediately." He reports that the ointment also helps the rash to "dry up" and also prevents spreading, which happens when he scratches.

Another reader living with the condition, who is allergic to steroids, has found relief with a hair dryer. By using a low setting that doesn't burn or damage his skin, he reports that the warm air not only relieves the itch for several hours, but also seems to cause the rash to retreat.

-- The column about the ick factor of the traditional colonoscopy prep solution brought a ton of mail. We have reached out to some colleagues here at UCLA who use an alternative approach and will be addressing the topic again in a future column.

-- And finally, a bit more about service dogs -- or more specifically, fake service dogs. We heard from many of you about the frustration of seeing people abuse the privileges extended to genuine service animals because they want to bring their pet into a store, restaurant or theater. Brad from Naples, Florida, wrote of a plane trip during which an unruly collie brought aboard as a service dog spent the entire flight barking and lunging at passengers.

It's true that some people are taking advantage of the honor system that gives service animals carte blanche to access public places. However, just because you can't "see" a person's challenge or disability doesn't mean the dog is a mere pet. For example, some people with diabetes or epilepsy, which are mostly invisible conditions, depend on their service dogs for warning of a medical emergency.

That said, we share your dismay when poorly trained, ill-mannered or aggressive animals are passed off as service dogs. Not only is it selfish and dishonest, it's also detrimental to the reputation of true service dogs, and makes things even more difficult for their owners.

(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: Some researchers say the main reason for many health issues today, including allergies and asthma, is that our children are kept too clean and have no resistance to anything. What are your thoughts?

Dear Reader: First, let's discuss the benefits of hygiene. The greatest boon to human longevity, at least in developed parts of the world, has been our ability to deal with wastewater. Separating humans from the waste they produce, and treating that waste, has decreased our susceptibility to a host of diseases. In Yemen, for example, the number of cases of cholera currently exceeds 800,000 due to the inability to manage wastewater. In fact, inadequate sanitation, combined with a limited ability to properly disinfect hands, is estimated to cause 4 percent of deaths worldwide.

But yes, there may be a risk to too much good hygiene. Humans live in symbiosis with the bacteria within and upon their bodies, and an inherent balance is necessary for a healthy life. This balance may extend to the bacteria in our environment, meaning that restricting our bodies from normal outdoor organisms may have a downside. The Amish in the United States, for example, live on farms and spend much of their time outside. Coincidentally, their children have much lower rates of allergies, eczema and asthma compared to non-Amish children who don't live on farms.

The evidence extends beyond that correlation. A 2017 study of adult farmers and their spouses compared their childhood exposure to a farm environment against their rates of allergies and asthma. Those who were exposed to farming as children were less likely to have allergies as adults. Further, those whose mothers worked on a farm while pregnant also had a lower rate of asthma and allergies.

Then there was a Swedish study on pacifier cleaning. Researchers found that the parental practice of cleaning a pacifier by putting it in one's own mouth before giving it back to the infant was linked to a lower rate of eczema and asthma in children at age 18 months. That same study also showed that vaginal birth, with its increased infant exposure to bacteria, was linked to a lower rate of allergies at 18 months compared to Caesarean delivery.

Other studies have shown that having an older sibling decreases a child's risk of allergies and eczema, supposedly because older siblings bring more bacteria into the house. Similarly, having a pet in early life (especially if it's a dog) has been linked to a lower rate of allergies and asthma in children.

But bacteria may just be one factor in the allergy equation. Exposure to allergens themselves may desensitize a child to them later in life. That brings us to the fact that children and their parents overall are spending less time outside. At the same time, children in densely populated urban areas are exposed to pollutants at younger ages. Both factors may increase the risk of allergies and asthma.

In summary, it's clear that the rates of asthma and allergies have incrementally increased in the United States over the last 50 years. Although the research is largely correlative, it seems equally clear to me that we can reduce that risk in our children by getting them -- and ourselves -- outside the house as much as possible, exposing them to their surrounding biome (within reason), and pushing for a reduction in pollution.

(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.)