It's the soap, not water temperature, that kills viruses

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 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 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.

Q: 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?

A: We've seen a boom in the popularity of health tracking devices in recent years. A poll conducted last year found that one in three 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.

• Dr. Eve Glazier is an internist and associate professor of medicine at UCLA Health. Dr. Elizabeth Ko is an internist and assistant professor of medicine at UCLA Health. Send your questions to askthedoctors@mednet.ucla.edu.