Hello, dear readers, and thank you for joining us for the continuation of our monthly letters column. We received so many questions related to the coronavirus and COVID-19 that we needed to address them.

-- A reader from Great Barrington, Massachusetts, asked if water temperature plays a role in killing the virus when we wash our hands. “I have been diligently washing my hands, but sometimes I don't wait for the water to come out hot,” he wrote. “Does washing with cold water and soap kill the germs, or does the water have to be hot?”

The answer is that the water you wash your hands with can be any temperature at all. Although warm water may be more comfortable, it’s the properties of the soap -- not the water temperature -- that breach the outer coating of the virus and kill it.

-- Along those same lines, a reader from Santa Rosa, California, urged people to consider turning off the tap during the 20 seconds they are lathering up. “Hand washing is critical for health now, but water conservation never fails to be significant,” she wrote.

-- A reader from Arkansas asked if using the microwave is a good way to destroy virus particles on surfaces. “I feel that the best way for the virus to invade my home in this rural and isolated area of Arkansas is through the mail and newspaper, and I have been running them through the microwave for 30 seconds,” he wrote. “Is the microwave killing the virus?”

A microwave oven works by exciting the water molecules in a food or beverage, which raises its temperature. The actual radiation doesn’t have a direct effect. Since viral particles are made up of proteins and fats, the microwave will not destroy them.

However, the most recent research shows that the major source of transmission of the novel coronavirus is through respiratory droplets, which are emitted while breathing, sneezing, coughing, speaking or laughing. And while viral particles have been found to persist on paper for up to 24 hours and on plastic for up to three days, the risk is quite low. There are no documented cases of that kind of transmission. If you’re still worried, you can use hand-washing or gloves to protect yourself until 24 hours have passed.

-- A reader from Indiana, who, like so many of us, is running low on hand sanitizer, asked about going DIY. “Will the homemade wipes be as effective in killing germs as the prepackaged brands?” she wrote. As long as the alcohol content in your formula is at least 60%, the minimum needed to kill most germs, your home brew will be effective. The only way to achieve this is by using isopropyl or rubbing alcohol that is 99% alcohol volume. Be sure to rub all hand sanitizers into your hands until they are completely dry, from 30 to 60 seconds.

Thank you again to all of our readers for your kind thoughts and well wishes. We hope you and your families stay safe and well.

(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 Doctors: I understand how my fitness tracker counts my steps and measures my heart rate, but supposedly it can say how well I sleep. How can it do that, and is that sort of data even accurate?

Dear Reader: We’ve seen a boom in the popularity of health tracking devices in recent years. A poll conducted last year found that 1 in 3 Americans has tried out some form of health tech, and that close to 20% of us now use a digital fitness tracking device each day. Depending on the specific device, wearables can count the number of steps we take each day, log our heart rate, analyze stress, count how many flights of stairs we have climbed, pinpoint the amount of time we’ve spent being active, estimate how many calories we’ve burned, measure distance traveled or use UV sensors to measure sun exposure. And, yes, a growing number of devices now follow us into the bedroom to monitor and analyze our sleep.

Many wearables, like the one you use, include a sleep mode. Again, depending on the device, they may offer information about how long you sleep, or about the quality of that sleep. They do this using sensors known as accelerometers, which can detect not only when someone is moving but also the speed and direction of that motion. This data, along with the heart rate information that the device collects, is extrapolated into sleep analysis. Some trackers even claim to be able to quantify how much time has been spent in the three major phases of sleep -- light sleep, deep sleep and REM sleep.

It’s important to note that for accurate sleep analysis, you need an overnight stay at a sleep lab. There, electrodes are placed on the face, scalp, chest and limbs to digitally collect and record a range of activities in both the brain and the body. The information that goes into analyzing your sleep includes breathing, physical motion, muscle tone, eye movement, heart rate and rhythms, and brain wave activity. Fitness trackers, by contrast, are limited to the motion and heart rate data that they are able to collect, which is then parsed by an algorithm. Sleep experts are concerned that someone with a sleep disorder who relies on the data from a fitness tracker may inadvertently be reassured that all is well. The flip side is that someone with no sleep problems at all may become worried about data that isn’t necessarily accurate.

The bottom line is that a fitness tracker with a sleep mode can be good at letting you know how long you were motionless, how often you were restless and how many times you got up during the night. However, it’s not information that reliably translates into sleep quantity or sleep quality. Anyone who thinks they may have a sleep disorder, or who wants to improve the quality of their sleep, should first check with their health care provider. Then, if it’s appropriate, a night in a sleep lab may be the next step.

(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.)

Hello again, dear readers! You’ve kept our digital and postal mailboxes even more full than usual with your questions, thoughts and (thank you!) kind words. Not surprisingly, much of the discussion focused on COVID-19. To help with the volume of mail, we’ll have a separate column with your virus-related questions next week. And now, onward to the more general discussion.

-- In a column about the search for a saliva test to diagnose Parkinson’s disease, we mentioned the lack of a specific diagnostic test for the condition at this time. A reader from Oklahoma, whose wife lives with Parkinson’s disease, wondered why a test known as a DaTscan wasn’t mentioned. “It is considered reliable enough that it is often required at the start of treatment testing to prove a patient has PD,” he wrote.

DaTscan uses a radioactive isotope to assess the health of the dopamine system in the brain. It’s the loss of dopamine transporters (DaT) that leads to the neurological symptoms of Parkinson’s disease. However, the scan will return an abnormal result in any neurological condition that involves dopamine transporters. It’s used in conjunction with a neurological and physical exam to arrive at a final diagnosis, but in and of itself does not return a definitive PD diagnosis.

-- A reader from Spokane who suffers from chronic foot pain requested a copy of our column about a condition known as Morton’s neuroma. Although we can’t mail you a copy, we can provide you with the link. We hope it helps. uexpress.com/ask-the-doctors/2019/12/9/having-a-mortons-neuroma-is-a

-- In that same vein, a reader from North Carolina is disappointed that her newspaper occasionally abridges our columns. The good news is that you can find the entire (and uncut) Ask the Doctors archive at uexpress.com/ask-the-doctors.

-- A reader whose 76-year-old mother has just received a diagnosis of colon cancer wonders where to learn about clinical trials looking into the disease. An excellent resource is The National Cancer Institute, at cancer.gov. Enter the words “colon cancer clinical trial” in the search bar, and the top three results will give you a wealth of information.

-- To the reader who asked what RNA and DNA stand for, the answer is ribonucleic acid and deoxyribonucleic acid, respectively. These are the names of the sugars that serve as the backbones of the two molecules.

-- A column about hypertension led a reader to ask us to highlight something known as “white coat syndrome.” This is a condition in which someone’s blood pressure spikes in a clinical setting but is otherwise normal. Although there is no surefire cure or mitigation for this, it’s important information for your health care provider to have. They may ask you to wear a portable blood pressure monitor for 24 hours to get an accurate reading.

We’ll wrap up with another thank-you, this time to the sharp-eyed readers who pointed out an error regarding dietary guidelines for daily limits on sodium. You’re correct that the unit of measurement should have been 2,300 milligrams, and not micrograms (sigh), as we wrote.

(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.)