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Infections from a drug-resistant fungus have been occurring around the world for the past decade. It's not cause for panic, but it's wise to understand the facts and ways to protect yourself.

Ask the doctor

Q. I think I have heartburn, but I hear that what feels like heartburn is sometimes a more serious condition. How do I know if I have heartburn?

A. You've asked an important question. "Heartburn" describes symptoms caused by the reflux of stomach acid up into the esophagus (the tube that carries food from the mouth down to the stomach). It is a burning sensation. You can feel it high in the abdomen, just below the bottom of the breastbone, or underneath the middle of the breastbone in the chest. In other words, despite the word "heart" in the word "heartburn," real heartburn comes not from the heart, but from the stomach and esophagus.

Arthritis, bunions, and gout can be disabling. Here are common fixes to stay mobile.

Aching hips, knees, and shoulders are common, and over time can lead to immobility. But so can an aching big toe. The joint at the base of the big toe � called the metatarsophalangeal or MTP joint � is the part of the toe that is affected.

What's the MTP joint?

The MTP joint connects the first long bone (metatarsal) in the forefoot to the first bone of the big toe (phalanx). The joint bends with every step you take, so that you can push off and let the other leg move forward. But the MTP joint takes a beating during that process: for a brief moment as you push off, the MTP joint supports half of your body weight.

On call

Q. After I have a bowel movement I sometimes get quite weak and have to lie down until the feeling passes. Why does this happen and is it cause for concern?

A. The sensation you are describing is most likely due to a reflex called a "vasovagal reaction." Here's what I mean.

Peripheral artery disease is serious but preventable.

As people get older, they sometimes shrug off painful cramping in their calves when they walk as a sign of age or overexertion. But it can be a symptom of a more serious condition known as peripheral artery disease, or PAD.

PAD is a condition in which fatty deposits collect in arteries outside the heart � most commonly in the legs � and reduce blood flow in that part of the body. Doctors used to think PAD mostly affected men, but when researchers began to include more women in their studies, they learned that the condition is just as common in women, affecting one in every 10 women over age 50 and one in every five over age 60, says Dr. Aruna Pradhan, a cardiologist and assistant professor of medicine at Harvard Medical School.

Q. I have read that people who have had their gallbladders removed should take bile salts. My gallbladder was removed many years ago, and no doctor has said I should take bile salts. Should I?

A. Bile salts are produced in the liver, secreted into the bile ducts and gallbladder, and sent from there to the small intestine by way of the common bile duct. In the intestine, bile salts make it easier for your body to absorb and digest the fats and fat-soluble vitamins that you've eaten. Remember, not all fats are bad: there are "good" fats, and they are crucial to our health.

Q. You wrote about weak, brittle fingernails with longitudinal ridges. I have strong nails with horizontal ridges. What causes this, and what can I do about it?

A. You may be referring to Beau's lines, which are grooves that run horizontally across the nail plate. They usually develop when nail plate growth, which begins in the nail matrix (located under the cuticle), is temporarily disrupted. This can occur with direct injury to the nail matrix; an inflammatory condition such as psoriasis; infection around the nail plate; repetitive picking at the nails or cuticles; or even a manicure. Systemic causes include a common side effect of chemotherapy, nutritional deficiencies, illnesses accompanied by high fever, metabolic conditions, and diminished blood flow to the fingers (from Raynaud's phenomenon, for example).

Q. For years, I have had recurrent cold sores and took antiviral drugs to treat the outbreaks. A friend suggested that I take daily lysine.  What's the evidence that it works?

A. Cold sores (sometimes called fever blisters) are painful fluid-filled lesions on or near the lips that are caused by the herpes simplex virus (HSV). There are two kinds of HSV: HSV-1, which causes most cold sores, and HSV-2, which is mostly responsible for genital herpes. HSV-1 infection is very common and easily transmitted by kissing or other contact with saliva. Once you're infected, the virus lays dormant in the nerve cells that supply sensation to the skin. When the virus becomes active, it travels to the skin surface and multiplies, causing an outbreak.

Ask the doctor

Q. A friend says that the worst disease of all is ALS. What is it?

A. What makes a disease the "worst?" For many, it would be a disease that robs them of their mind. For others, it would be a disease that creates constant pain. For still others, it would be a disease that makes them unable to care for themselves or to control their bodily functions � in full view of their family and closest friends.

It might be orthostatic hypotension, a condition that can be challenging to catch and treat.

You stand up and suddenly feel unsteady on your feet. It's easy to brush off this experience as a fluke or a bug, but don't. You may have a condition called orthostatic hypotension, a temporary drop in blood pressure when you stand. It's tricky to catch.

"Blood pressure is highly variable, and depends on position, timing, the method of measurement, and circumstances associated with its measurement," says Dr. Lewis Lipsitz, chief of gerontology at Harvard-affiliated Beth Israel Deaconess Medical Center and director of the Marcus Institute for Aging Research at Hebrew SeniorLife. "It may take multiple blood pressure measurements at different times of day, lying and standing, in order to detect orthostatic hypotension," Dr. Lipsitz says.