Dear Doctor: My husband and I enjoy a glass of wine with dinner. I prefer red wine, but it always gives me a bad headache. It happens from even half a glass, so I know it’s not a hangover. I thought it was the sulfites, but I hear there’s a new theory. Do you know what that is?

Dear Reader: For some people, a glass of red wine is one of life’s small pleasures. For many others, it’s the trigger for a painful headache. An analysis of responses to health questionnaires found that while alcohol in general was associated with non-hangover headaches, red wine was cited most often as the specific cause. Research into the question found that up to one-third of people say that they get a pulsing, pounding headache after drinking red wine, sometimes as soon as within 30 minutes of consumption.

While the existence of red wine headaches has proven easy to pinpoint, the reason why has remained elusive. One theory focused on a sensitivity to histamines, an organic compound whose chemical structure is similar to ammonia. The histamines produced by our bodies are used in intracellular communication. They aid in sleep regulation, are important to brain function and play a role in allergic response. Histamines are also abundant in some fermented foods, including red wine. Sulfites, a preservative commonly used in wine, were also seen as a potential culprit. But when studies found that red wines without sulfites, and those low in histamines, also triggered the dreaded headache, the search for an answer continued.

Last year, researchers from the University of California’s Davis and San Francisco campuses suggested a potential new cause for the red wine headache: a class of organic compounds known as flavanols. These occur naturally in a wide range of plants, and their antioxidant properties play a role in cardiovascular health. Foods rich in flavanols include berries, walnuts, dark chocolate, tea, coffee and, yes, red wine.

When it comes to a link to red wine headaches, the researchers pointed to a specific flavanol called quercetin. It is produced in red grapes as they are exposed to sunlight. Quercetin impedes the body’s ability to completely metabolize alcohol. This results in the buildup of a compound known as acetaldehyde. Although small amounts of acetaldehyde are manageable, accumulations can become toxic. The researchers suspect this may be the mystery compound behind the red wine headache.

Until this new theory is proven, red wine drinkers susceptible to getting headaches will have to take evasive measures. These can include taking a defensive dose of an over-the-counter anti-inflammatory medication before drinking, or choosing a white or rose wine, each of which is low in quercetin. If opting for a painkiller, it is important to know that both ibuprofen and acetaminophen can raise the risk of liver damage and gastrointestinal bleeding when mixed with several glasses of wine. And considering that the health risks of drinking alcohol extend well beyond a headache, a glass of sparkling water can be the wisest alternative.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10960 Wilshire Blvd., Suite 1955, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)

Dear Doctors: My sister and I are roommates, and we are both back to in-person work. We keep getting sick because co-workers with the flu won’t stay home and aren’t careful. I doubt we are the only ones wishing for a code of good behavior for when you’re sick. Can you talk about that?

Dear Reader: We agree that the concerns you have raised, along with the sense of frustration, are shared by many people. Whether it is in an office environment, a social gathering or the many public places people visit throughout the course of a day, just a moment of contact with someone in the infectious stage of an influenza infection can seal your fate for the next few weeks. For anyone, living through a case of the flu is deeply unpleasant. But for older adults, infants and people with weakened immune systems, a respiratory illness can pose a real danger. All of which makes it important to abide by the rules of good flu etiquette.

It is important to remember that the flu is extremely contagious, particularly in the early days of the illness. Someone standing just 6 feet away from a cough or a sneeze can become infected. The droplets that are emitted, which contain live virus, can hang in the air for more than an hour. They also land on surfaces, where the virus can persist for many hours. That puts people at risk of infection long after the individual who is ill has left.

The first rule of good flu etiquette is to stay home. Someone with the flu can spread the illness a day or so before symptoms appear, and for up to a week after. Over-the-counter medications can ease symptoms, but even though you may feel better, you are still actively infectious. Be kind to your body as it rallies the immune system to fight the viral invaders. Rest, drink plenty of fluids, eat nutritious meals and get plenty of sleep.

Throughout the course of a bout of the flu, take protective measures. Remember to wash your hands, as it is easy to spread the virus to anything you touch. The most common surfaces are doorknobs, light switches and cabinet handles. It’s a good idea to set a dedicated wastebasket for used tissues. Use a plastic liner, and seal it up when you dispose of the contents. Cover your mouth and nose when you cough or sneeze, as that pumps live viral particles into the air. Make an effort to socially distance, particularly at the start of an illness.

When you do get back to your regular routine, stay vigilant. Using a mask will protect the people around you. Arm yourself with hand sanitizer and plenty of tissues. It’s also a good idea to let people know that you have recently been sick. That gives both of you a graceful way to postpone the handshake or hug or kiss that may be your usual greeting. And if you haven’t yet, please get a flu shot. It lowers the risk of infection -- and also of severe illness.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10960 Wilshire Blvd., Suite 1955, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)

Dear Doctors: I just turned 65, and my doctor wants me to have a bone density test. What is it, and how does it work?

Dear Reader: A bone mineral density test, or BMD, measures the strength of one’s bones. It’s an important diagnostic tool for osteoporosis, a progressive disease in which bones become brittle and fragile and can easily break.

Although our bones appear hard and static, they are made up of living tissue. The honeycombed inner framework of a bone is composed of collagen, which is a protein. A mineral known as calcium phosphate provides strength and solidity. Together, these two substances create a strong and flexible structure that successfully withstands stress.

Our skeletons have a dynamic life cycle in which old bone is continuously removed, while at the same time new bone is added. In children and teens, the addition part of the cycle outpaces removal, allowing the skeletal bones to grow in both strength and density. This cycle peaks sometime in our late 20s, at which point bone reabsorption gradually begins to overtake bone formation. Certain hormonal changes that occur in women during menopause further accelerate that imbalance. The result is that old bone may be removed too quickly, new bone may be added too slowly, or both. Over time, the honeycomb framework within the bone grows increasingly porous, while the exterior structure becomes thinner.

All of this leads us back to the scan your doctor has recommended. Known as a DXA test -- that’s short for dual-energy X-ray absorptiometry -- it’s essentially the same procedure and technology used in a standard X-ray. A machine delivers low-dose X-rays, which measure the amount of calcium and other bone minerals present in a segment of bone. The proportion of bone minerals to soft tissue reveals bone density.

The DXA test, which is most often used to measure bone density at the hip and the lumbar spine, is used to diagnose osteoporosis. It can also help assess risk of future fractures, and to detect whether a treatment for osteoporosis is working. The test, which is as quick and painless as an X-ray, is performed on an outpatient basis. It takes from 15 to 30 minutes to complete, depending on the part of the body being scanned. The results of the test, known as a T score, are presented as a comparison between your own bone density and that of a young adult at the peak of bone formation. A second measurement, known as a Z score, compares your bone density to people your own age, size and gender.

The BMD test is usually recommended for women when they turn 65. It may be recommended earlier than that if a woman has rheumatoid arthritis, low body weight or low vitamin D levels; has used a corticosteroid for three or more months; has a family history of osteoporosis; has experienced bone breaks resulting from a minor accident; has lost height; or is a heavy smoker or drinker. Depending on the results of the initial test, a follow-up test may be needed in one or two years.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10960 Wilshire Blvd., Suite 1955, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)