Dear Doctor: Why do you have to wash your hands with soap and warm water for at least 20 seconds? Are they not getting clean if you’ve only got cold water? And why is 20 seconds the magic number? What about hand sanitizers?

Dear Reader: Handwashing is in the news right now due to the coverage of the new coronavirus, COVID-19, as well as our ongoing flu season. It’s an important topic because, although the exact means of transmission of the new coronavirus isn’t clear yet, we do know how influenza spreads, and COVID-19 is likely to be similar.

In addition to inhaling aerosolized droplets from an infected person’s cough or sneeze, influenza spreads through contact with surfaces that have been contaminated by the virus. This can be direct contact, such as when you shake hands with someone infected with the virus, or indirect contact via a contaminated surface or object. If you come into direct contact with the virus and then touch your own mucous membranes, you risk infecting yourself. This includes rubbing your eyes, nose or mouth; biting your nails; eating with your hands; dabbing on makeup; or just resting your chin in your hands. All of this leads to two bits of important advice -- don’t touch your face, and do wash your hands. The first relies on awareness, while the latter is all about technique.

Start by wetting your hands with clean, running water. The temperature of the water doesn’t play a role in efficacy; it’s just that warm water is more comfortable to use. If cold water is the only option, that’s fine. What matters most is that you work up a lather with soap -- any kind of soap will do -- and carefully clean all of the surfaces of your hands. Be sure to wash the palms and backs of the hands, the fingers, the knuckles, the webs between the fingers and the areas around and beneath the nails. Doing this carefully and thoroughly, with gentle pressure to create friction, takes in the neighborhood of 20 seconds. Then rinse well and dry thoroughly. Frequent handwashing can dry out the delicate skin on your hands, so carrying a travel-size moisturizer can be a good idea.

As for hand sanitizers, studies have shown that although they can be helpful, washing with soap and water is the most effective at removing a variety of pathogens. Hand sanitizers may not be as effective when used on hands that are dirty or greasy.

When using a hand sanitizer, it’s important to choose one that is alcohol-based, at a concentration of no less than 60%. The product label will state the concentration of alcohol. Don’t skimp. Always use the amount of sanitizer that the label recommends. Then spread the liquid over all of the surfaces of your hands and rub gently until they are dry.

Hands clean? You’re not quite done yet. There’s another object that that makes frequent contact with your hands and face -- your phone. Check manufacturer directions, and add cleaning your phone to your daily routine.

(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: How do I know if I need a hip replacement? My right hip gets so stiff after I’ve been sitting at work for a few hours that I can hardly walk, and then it aches for the rest of the day and night.

Dear Reader: The hip is one of the largest weight-bearing joints of the body. Its unique structure lets humans stand and walk upright and gives our legs and torso an impressively wide range of motion. It is a ball-and-socket joint, which means that the rounded head of a bone fits neatly into a cuplike hollow. In the case of the hip joint, the ball-shaped head of the femur, which is the upper leg bone, sits inside a socket within the hip, known as the acetabulum. The surfaces of the femur and the hip socket are lined with cartilage, a smooth and springy connective tissue that cushions the joint and helps reduce friction. A membrane known as the synovium produces a thick liquid that lubricates and nourishes the interior of the joint. Fluid-filled sacs known as bursae act as cushions and protect the muscles and tendons as they move over bony areas within the joint. Muscles, ligaments and tendons anchor the hip joint and provide power, stability and flexibility.

The most common reason for a hip replacement is damage to the parts of the joint that reduce pressure and eliminate friction. This often occurs due to osteoarthritis, a degenerative condition in which the tissues of the joint begin to deteriorate, and rheumatoid arthritis, a chronic inflammatory disorder. Injuries, fractures, wear-and-tear due to overuse or being overweight, and cancer, while less common, also can lead to the need for a hip replacement.

One of the main symptoms that the joint may need to be replaced is significant and persistent pain. This occurs while walking, sitting, standing or bending over, and often is severe enough to wake you from sleep. It interferes with the ability to carry out daily activities and impairs quality of life. Imaging tests that reveal arthritis, or damage to the bone or tissues of the joint from other causes, also may signal the need for joint replacement.

A hip replacement is major surgery. It entails removing the damaged or diseased tissues and replacing them with an artificial joint. Post-surgical physical therapy is a big part of a successful outcome, and full recovery can take from six months to a year. It is important to note that the new joint lasts about 15 years, after which it will need to be replaced again. Before diving into the deep end, your health care provider is likely to ask you to explore noninvasive interventions. These include rest, physical therapy, weight loss, using a cane and a range of anti-inflammatory or pain medications. If these fail to provide adequate relief, or if the medications are not tolerated, then a new joint may be the best option.

If you do opt for a hip replacement, find a reputable and experienced surgeon. You want someone who is board certified in orthopedic surgery, specializes in hip replacement, has experience with your specific condition and accepts your insurance.

(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: Our sister saw her doctor because her chest felt “heavy,” and he found fluid in her lung. Further tests showed lung cancer, which had already spread. She never coughed, and she quit smoking years ago. What are some of the symptoms of lung cancer?

Dear Reader: Although a cough can be an indication of lung cancer, it is not the only sign of the disease, and it doesn’t appear in every case. Lung cancer can take years to develop; in its earlier stages, people may have no symptoms at all. When the disease does begin to make itself known, some of the symptoms can be unusual, and, thus, not immediately associated with lung cancer.

Let’s start with a cough. It’s one of the more common symptoms of lung cancer, and it appears in up to half of all patients. This can be a new and persistent cough that isn’t associated with a cold or the flu, or it can be a chronic cough that gradually becomes worse. These coughs may be painful, and they may produce red or rust-colored phlegm or sputum, which indicates the presence of blood. Any time that you cough up blood -- whether it is bright red, which indicates new blood, or a darker hue, which signals old blood -- it’s important to see a doctor.

The presence of fluid, as in the case of your sister, is known as pleural effusion. It’s not actually inside the lungs, but in an area between the lungs and the chest wall, which is known as the pleural space. When it is associated with cancer, the condition is known as malignant pleural effusion, and it is a sign that the disease has spread. The buildup of fluid in the pleural space causes the sensation of heaviness that your sister reported, sometimes also described as a feeling of tightness. Often, it is accompanied by shortness of breath, a dry cough and exhaustion. Pleural effusion can be life-threatening, and the fluid must be drained.

Additional symptoms of lung cancer include chest pain, hoarseness, frequent bouts of bronchitis or pneumonia and persistent chest pain. Symptoms of the disease that are not lung-related include persistent fatigue or malaise, loss of appetite, unexplained weight loss, swollen or enlarged lymph nodes and shoulder or upper-back pain. Some patients develop an enlargement of the fingertips, known as clubbing. It’s important to note that each of these, including cough, can be caused by other conditions.

For adults who are at a higher risk of developing lung cancer, the recent development of an early stage screening test has been an important advance. Known as low-dose computed tomography, or a low-dose CT scan, it’s recommended for adults between the ages of 55 and 80 who are heavy smokers, or who were heavy smokers and quit less than 15 years ago. The scan, which uses a small amount of radiation, makes a detailed image of the lungs. Risks of the test include false positives, which can lead to unnecessary surgical procedures, and exposure to radiation, which itself can cause cancer. Anyone interested in the test should check with their doctor to see if they meet the screening criteria.

(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.)