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.)

Dear Doctor: My wife overindulged on her birthday and wound up with a pretty fierce hangover -- headache, nausea, brain fog, the works. She got so much weird advice that it got us to wondering, what exactly is a hangover? Are there any remedies that actually work?

Dear Reader: Your question is one for the ages -- literally. References to the unique state of distress we call a hangover date back thousands of years. So does the quest for a cure. Yet despite the best efforts of modern science, the cause of a hangover -- as well as a remedy -- remains unclear.

Let’s start with what we do know. A hangover occurs when you drink too much alcohol. For some, a few glasses of wine can lead to profound regret the morning after. For others, getting a hangover takes a night of excessive drinking of hard liquor. No matter the amount of alcohol, the symptoms remain the same. These include the headache, nausea and cognitive issues that your wife suffered from, as well as dry mouth, thirst, fatigue, dizziness, vertigo, diarrhea, tremors, disturbed sleep, rapid heartbeat, excessive perspiration, anxiety, low mood and sensitivity to light and sound.

Research suggests that genetics play a role in how much you can drink before you’ve earned yourself a hangover. So do a person’s age, sex and physical health; the state of their immune system; and how quickly they drink. The specific type of alcohol may also be a factor. Darker-colored drinks -- such as bourbon, dark beer and red wine -- contain higher concentrations of compounds known as congeners. The body metabolizes these into toxic substances such as formaldehyde and formic acid, which can add to hangover misery.

Dehydration was long considered a prime culprit in hangover symptoms, but recent research has found no difference in electrolyte levels among people who are hung over and those who are not. Although a toxic compound known as acetaldehyde, produced when the body breaks down ethanol, had been implicated in hangover misery, more recent research now points to the role of cytokines. These are small proteins associated with inflammation, which the immune system uses for signaling. The theory is that drinking triggers the release of cytokines, which in turn unleash the full fury of the immune system.

As for how to cure a hangover, science hasn’t gotten that far. The best you can do is manage the symptoms for the eight to 24 hours it takes for a hangover to play out. First, skip hair-of-the-dog therapy. More alcohol may give a temporary boost, but soon enough leads to the throes of even more misery. Instead, drink plenty of water, eat complex carbs to boost low blood sugar and fend off nausea, use antacids if needed for stomach upset, and get some sleep. Aspirin and other non-steroidal anti-inflammatories can help with headache, but can also irritate the stomach. Never take Tylenol during or right after drinking, as it can cause liver damage when mixed with alcohol. No one who has ever had a hangover wants to hear this, but the only certain cure is time.

(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.)