Dear Doctor: I smoked cigarettes for years, but I always used the filtered kind. (I've since stopped.) Now I'm hearing that people who smoke filtered cigarettes have increased rates of lung cancer compared to those who smoke unfiltered cigarettes. How can this be?

Dear Reader: First of all, let me congratulate you for kicking the habit. No doubt it was hard, but giving up smoking was the best thing you could have done for your health. By doing so, you decreased not only your risk of lung cancer and emphysema, but also your risk of a heart attack and vascular disease.

That said, I agree; at first glance, it doesn't make sense that filtering the tar from cigarette smoke can increase the risk of lung cancer. The cigarette industry, knowing the health risks of smoking tobacco, invented the filtration system in the 1950s specifically to reduce smoking-related injury to the lungs. In the late 1960s, only 7 percent of cigarettes had a filtering system, but by 1982, nearly 100 percent of cigarettes had a filtering device.

Prior to unfiltered cigarettes, the majority of lung cancers were squamous cell cancers. Because smokers at the time were predominantly male, these cancers were largely found in men. As filtered cigarettes became the predominant cigarette on the market, the rates of another type of lung cancer, adenocarcinoma, began to increase. During this same time period, women began smoking at greater rates, and these cancers were often the predominant type among female smokers.

In fact, rates of lung cancer in women have consistently been increasing since the 1970s, and the majority of these cancers have been adenocarcinomas. Further, while the overall rate of lung cancer in men has decreased over the last 40 years, the percentage of men with adenocarcinoma has increased.

Those facts establish a correlation between filtered cigarettes and adenocarcinoma of the lung. But a direct connection is less clear. After all, filtered cigarettes do substantially reduce the amount of inhaled tar. In 1954, a cigarette delivered 38 milligrams of tar; in 1997, it delivered 12 milligrams of tar. Cigarette companies even advertised the fact that filtered cigarettes delivered less tar, calling them "light" or "ultralight" cigarettes. That sounds good, doesn't it?

Note, however, that the filters themselves can lead smokers to take bigger inhalations to overcome the filters. Thus, they inhale more of the toxic substances and cancer-causing materials in the cigarettes. Additionally, filtered cigarettes burn more slowly, leading to more puffs per cigarette and the inhalation of more toxic substances. Also, without the high heat of unfiltered cigarettes, toxic substances are less likely to burn off. And finally, a cigarette filter -- based on where it sits upon a person's lips -- leads to increased water content within the filter, which enables toxic particles to move more easily into the lungs.

All these factors mean that toxic chemicals, such as nitrosamines and NNK, which have been linked to lung adenocarcinomas, are more likely to travel deeper within the lungs of people smoking filtered cigarettes than those smoking unfiltered cigarettes. Research has not yet proved that filtered cigarettes lead to higher rates of adenocarcinoma, but the Surgeon General's 2014 report suggested that cigarette design changes in the 1950s may indeed have led to the rise in adenocarcinomas of the lung.

Ultimately, the fact remains that cigarettes are extremely addictive -- and filters don't change that fact. With or without filters, cigarettes cause lung cancer. So the best course of action is to stop smoking (or to never start) and to not believe that a filter will decrease your risk of lung cancer.

(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: My boyfriend wants to take me to his favorite Thai restaurant, but I'm a little worried; Thai cuisine uses a lot of peanuts and I'm allergic. For people with food allergies, how dangerous is it to eat meals made with equipment also used to cook allergen-containing foods?

Dear Reader: Food allergies in the United States appear to be on the rise, which makes your question increasingly relevant. For individuals with allergies, even a tiny amount of the allergen can set off a reaction. This includes consuming food that doesn't actually contain the problem ingredient, but has been produced on equipment where the allergen is present in some form. This is known as cross-contact, and it can cause serious problems.

If you accidentally consume a food that your immune system has identified as dangerous, you're in for a physical reaction. This can be as mild and manageable as itchy skin, a headache or an upset stomach, or as severe as anaphylaxis, which can lead to death.

Although the steady uptick in allergies is worrisome, the newest research, which analyzed data from the medical records of 2.7 million patients, actually dials back the previous estimate of people with food allergies in the U.S. Instead of the widely quoted 5 percent, this study pegs the number at an average of 3.6 percent.

More women (4.2 percent) than men (2.9 percent) have food allergies. Asians had the highest incidence at 4.3 percent. Latinos had the lowest rates at 2.8 percent. Still, identifying and diagnosing a food allergy can be difficult, so all estimates are just that -- a researcher's best guess.

Your peanut allergy is in the top five of food reactions. Shellfish is first, followed by fruits or vegetables, dairy, then peanuts. Needless to say, the range of foods that can cause an allergic reaction is far more diverse.

To help people with allergies, the U.S. Department of Agriculture requires food labels to clearly identify the presence of any of the major food allergens. Also, if a product uses nuts, the specific nut must be named. But -- and this is important -- the "this product may contain" language on a food label, which warns of possible cross-contact, is voluntary. That means the absence of that warning doesn't necessarily eliminate the chance of cross-contact.

When it comes to dining out, where the preparation of your food is out of your control, your best defense is to be your own advocate. Call ahead to the restaurant and ask to speak to the chef or manager about your concerns. Ask for details about the precautions the restaurant takes to prevent any trace of an allergen from finding its way to your plate. (You'll get the most relaxed response when you call during off-peak hours.)

During spur-of-the-moment restaurant visits, enlist the aid of your server. Clearly explain what you're allergic to and how it may affect you, and ask him or her to let the kitchen know as well. Find out how the kitchen handles potential cross-contact. And, because we live in an imperfect world, please remember to always carry an EpiPen.

(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 know of several older women who have died within a year after a hip fracture. But why? Is this due to a cause and effect of a bone fracture, or something else entirely?

Dear Reader: Hip fractures are common as we get older. The lifetime risk of a hip fracture in a woman is 17.5 percent; for men, it's 6 percent. Women have greater rates of osteoporosis than men and thus the greater risk of fractures. Now let's look at why hip fractures increase the rate of death.

Let's start with the most common reason for an older person to get a fracture -- a fall. Such a fall doesn't usually occur from hiking mountainous terrain, but rather from a misstep or a loss of balance within the home. In fact, 90 percent of hip fractures in the elderly occur because of a fall from a standing position. The loss of balance that precipitates a fall occurs because of weakness in hip girdle muscles, and/or generalized weakness due to illness, medication and/or a prior stroke. To put it simply, the more debility one has, the greater their chance of falling; the hip fracture is often the consequence of that debility. So this debility, in itself, can be a major reason for the increased death rates seen among people with hip fractures.

Next, the majority of displaced hip fractures will require surgery to repair. The surgery can be either a total hip replacement or a surgery to bring the misaligned pieces of bone together using metal screws, rods and plates. Surgeries are fraught with possible complications, leading to a greater risk of debility and even death. Complications include blood loss, cardiac arrest, stroke, problems with anesthesia, infection and blood clots.

However, waiting too long to have a surgery for a hip fracture can also lead to prolonged bedrest, resulting in an increased chance of blood clots in the legs, bed sores, urinary tract infections, pneumonia and, again, death.

Another problem, before and after surgery for a hip fracture, is that elderly patients are especially likely to become delirious. One study found that 61 percent of elderly patients with a hip fracture had an acute state of confusion. This confusion leads to greater agitation, an inability to eat and limited ability to recover from a hip fracture. In addition, confusion can lead to medications to sedate an agitated patient, further delaying recovery.

For some, recovery from a hip fracture can take months. Long hospital and rehabilitation facility stays lead to an even greater risk of complications.

When you add pre-fracture problems to post-fracture problems, it's no surprise that the mortality rates are so high. A 2017 European study found that, in people older than 60, 15.1 percent of 463 patients died within one year of a hip fracture. A 2010 American study of the same age group found that 21.2 percent of 758 patients died within one year of a hip fracture.

So prevention is crucial. Regular exercise, use of calcium and maintaining good vitamin D levels are absolutely necessary. So is good overall health. Encourage it in yourself, and do what you can for those you love.

(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.)