Q. Why do the public health authorities keep telling us to always wear a mask? I have not seen any information showing that masks stop the spread.

Instead, most of the info I have read says cloth masks do not block small aerosol particles. But they cut needed oxygen intake and raise CO2 intake.

A. Masks do not provide 100% protection, but they are much better than nothing. The Centers for Disease Control and Prevention reported a case in which two hairstylists in Springfield, Missouri, developed symptoms of COVID-19 (MMWR, July 17). Both continued to cut hair while wearing masks. They interacted with 139 clients who also wore masks. None of the clients who was tested came down with COVID-19.

In addition, a study in a large Massachusetts hospital system found that when both patients and staff all wore masks, the rates of COVID-19 infection dropped dramatically (JAMA, July 14). In commenting on this research, public health experts point out that face masks serve two purposes: They protect the wearer against inhaling droplets and even some aerosol particles. They also trap particles being exhaled by infected individuals (JAMA, July 14). As a result, universal masking can help cut transmission.

As for oxygen and CO2, a recent study found that face masks do not reduce oxygen nor lead to carbon dioxide buildup (Annals of the American Thoracic Society, Oct. 2). This held not only for healthy volunteers, but also for those with COPD, which makes it much harder for people to breathe.

Q. I’ve been taking metoprolol for about 10 years. At first, I was doing fine on a generic made by Par. Then the pharmacy switched to a different generic supplier. After a few doses, my heart started to race, and I once again had arrhythmias. The cardiologist’s office is trying to get my insurance to authorize brand name Toprol XL. Without insurance, there is no way I can afford the brand name.

A. We have heard from other readers that some generic metoprolol formulations do not work as expected. A racing heart rate is a dead giveaway that your beta blocker is not performing properly.

If you cannot get the insurance company to cover brand name Toprol XL, you might want to ask the pharmacy if it will order your metoprolol from Lannett. This generic manufacturer sells the authorized generic version of Toprol, so it should be identical to the brand.

You can learn more about authorized generics (which should be covered by insurance) as well as affordable brand-name products from Canada (not covered by insurance) in our eGuide to Saving Money on Medicines. Look for this online resource in the Health eGuides section at peoplespharmacy.com.

Q. Instant glue is the only effective treatment I’ve found for split thumb tips and fingertips. I have suffered every winter for nearly a decade. The pain is intense, so bad that I can’t even swipe my phone screen or button a shirt or type on a keyboard.

Lotions don’t work quickly, and most just cause more pain. O’Keeffe’s Working Hands helps, but only if I use it every single night.

A drop or two of instant glue takes the pain away within minutes. That’s long enough for the split to heal itself in most cases. The same active chemicals are found in liquid bandage, but glue costs much less and lasts longer. It keeps the wound sealed and clean, too.

A. Many readers agree with you on the value of instant glue for sealing cracked fingertips. Unlike liquid bandage, though, instant glue is not approved for this use.

In their column, Joe and Teresa Graedon answer letters from readers. Write to them in care of King Features, 628 Virginia Drive, Orlando, FL 32803, or email them via their website peoplespharmacy.com. Their newest book is “Top Screoctors Make and How to Avoid Them.”