Hello, dear readers, and welcome back to our monthly letters column. We hope you’re all doing as well as possible during these challenging times. We’ve received even more mail than usual, much of it -- no surprise -- virus-related. We’ll address some of those questions here, and the rest in an extra letters column soon.

-- Many of you have remarked upon the wide variety of facial coverings people are using and wonder if they are equally effective. The answer, unfortunately, is no. Coverings such as bandanas and scarves, which have a loose weave and a loose fit, don’t provide as effective a barrier as masks made of tightly woven fabrics, with multiple layers and a snug fit over the nose, under the chin and around the sides of the face. The goal of a face mask is to block the large droplets generated by a cough or a sneeze, as well as the airborne particles, known as aerosols, that we produce as we speak and exhale. That’s also why, although they are more comfortable to wear, masks fitted with valves are largely ineffective at protecting others from exhaled breath.

-- Speaking of face coverings, we had several questions about water temperature for washing reusable masks. “I always thought it was the soap, not the water temperature, that did the work when washing hands,” a reader wrote. “So why do all the articles say to wash your face mask in the hottest water possible?” You’re correct that it’s the molecular properties of soap that penetrate the fatty lipid membrane of the virus and disable, or “kill,” it. Water temperature doesn’t play a role, except in comfort. Guidelines from the Centers for Disease Control and Prevention recommend that people wash their masks with warm water and detergent. Water has to be very hot -- 140 to 150 degrees Fahrenheit -- to kill a virus on its own. What’s equally important when washing a mask is to dry it thoroughly, preferably in the dryer. Damp cloth gives other microorganisms, such as bacteria and fungus, a place to thrive.

-- In a column about chondrocalcinosis, a painful buildup of calcium crystals within the joint (also known as pseudogout), we mentioned that low doses of an anti-inflammatory called colchicine can be helpful. A reader from Kelso, Washington, wrote to say the medication brought her relief. “I have had this condition in my knees, ankles and even my wrists,” she wrote. “I started taking colchicine and had an immediate easing of pain, which finally went away.” We’re glad to hear that you found some relief from a painful condition. It’s important for readers to note that colchicine is available only by prescription. It can have side effects, and should be taken under medical supervision.

As always, thank you to everyone who took the time to write to us. Even though we can’t respond to each of your letters, we do read all of them. As a reminder, we can’t offer a diagnosis, recommend or comment on medications or provide a second opinion. Many of you continue to ask for copies of previous columns. The complete archive is available at uexpress.com/ask-the-doctors.

(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: I heard about a place in Australia where there’s suddenly a whole bunch of cases of flesh-eating bacteria. What kind of bacteria is this? Can something like that happen here in the United States?

Dear Reader: You’re referring to an outbreak of a tropical disease called Buruli ulcer, which has been centered along a portion of Australia’s southern coast. The disease is caused by a pathogen known as a mycobacterium. That’s the same genus of microorganisms that cause tuberculosis and leprosy, among other illnesses.

For fellow science nerds, the organism that causes Buruli ulcer is the mycobacterium ulcerans. It’s named for Buruli county in Uganda, which is where scientists first identified the collection of symptoms as a specific condition. The organisms that cause the disease release a unique toxin known as mycolactone. It not only damages the tissues it inhabits, but also is able to prevent the immune system from mounting a defense.

Buruli ulcer usually begins quietly, often with a small and painless raised lesion, a patch of thickened skin or an area of swelling just below the skin. Within the next four or five weeks, the organisms create a wound that, if left untreated, will grow in size. Although damage is usually limited to the skin and the tissues just below the skin, in some cases the bone can be affected. This can lead to deformities. About half of cases of Buruli ulcer are found on the lower limbs, about one-third appear on the arms and the rest develop in other regions of the body. How the disease is transmitted is not yet known.

Even though health care providers familiar with the disease can often make a diagnosis from viewing the damage caused by the microorganism, it’s important to conduct a thorough examination to rule out other potential causes. This includes taking the person’s medical history and learning about all recent travel. Tissues from suspected sores and lesions are gathered, either with a swab or a biopsy, and are then tested in a laboratory. In its early stages, the condition is occasionally mistaken for boils, fatty tumors known as lipomas or a fungal infection. Several of the people in Australia who became infected with the mycobacterium initially thought the resulting nodules were insect bites. The disease is treated with a combination of several different antibiotics and wound care.

Buruli ulcer has been identified in 33 different countries, but historically has been most common in certain tropical regions of west and central Africa. Outside of Africa, the largest number of cases each year are reported in Australia. The number of cases worldwide fluctuates. Reports have ranged from a height of 5,000 cases per year to a low of about 1,900 cases, in 2016. Now, as with the outbreak in Australia, cases appear to be on the rise again. As for whether or not the disease can become a problem in the U.S., it’s unlikely. Only a few cases have been reported here over the years, and each was linked to travel in a region where the organism that causes the disease is regularly found.

(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 city requires face masks now, and we’re not sure what’s the best kind for our kids. Our teen wears an adult mask, but we have a 6-year-old and a 9-year-old as well. Do you have any advice?

Dear Reader: We’ve been getting this question a lot as various state and city lockdowns end and we’re all peeking out from our quarantine bunkers. There’s no question that face masks are a vital tool for a safe reentry into public life. They do a good job at blocking our exhaled breath, which helps prevent the spread of the novel coronavirus in people who are infected. That said, there are a few caveats. Face coverings should not be worn by children younger than 2 years old, by anyone who has trouble breathing, or by anyone who is unable to remove the mask without assistance from someone else.

The best type of face mask for kids is the one that the child will wear. That’s going to be your guiding principle. Don’t worry too much about details such as the type of material the mask is made of, how it attaches or whether or not it has a filter. The bottom line is that if it’s not comfortable, your child won’t wear it properly. They’ll tug and pull at it or try to readjust it. In the process, they’ll wind up touching their faces, which increases the risk of infection. Even with an optimal mask, a younger child may not be able to tolerate it for extended periods of time. If that’s the case, prioritize mask use for situations when social distancing isn’t easy to maintain. Wearing a mask is particularly important indoors, where people tend to crowd together and where the virus can linger.

As for the masks themselves, they are effective only if they cover both the nose and the mouth. Look for one that’s fitted with a flexible clip on the nose piece. That makes it easy to adjust and customize to your child’s face. Avoid masks with a one-way valve. These allow the exhaled air to escape and do nothing to protect the people around you. Choose a mask that fits over the chin and reaches around the sides of the face. Not only will this give a more secure and comfortable fit, it helps cut down on the amount of air that blows out of the mask, rather than diffusing through the fabric.

If your kids are anything like ours, they have definite opinions about what they like to wear. Giving them a say in choosing their own masks can boost the odds that they’ll actually wear them. Look for washable masks made with two layers of breathable cloth. It may take a few purchases to find the mask your kid prefers. Once you do, get at least two masks per child so it’s easy to keep them clean. Teach kids to avoid touching their faces once the mask is on, and to clean their hands thoroughly once it’s removed.

(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.)