Q On a recent flight from Phoenix, I was selected to have my palms swabbed by the TSA. Then they told me my hands tested positive for explosives and put me in a room and searched me from head to toe. Of course, they found nothing. The agent told me it must have been the Lubriderm hand lotion I used that set off the false positive. How can this happen?

A It is not an urban legend. Lubriderm, like many lotions and creams, contains glycerin, which in some cases can set off sensitive airport Explosive Trace Detection swab machines, the TSA tells me.

Harmless glycerin is a component of nitroglycerin, used in explosives.

Other things that the Transportation Security Agency acknowledges can cause an ETD hand swab to read positive for explosives: using nitroglycerin heart medication, being exposed to fertilizer (on a golf course or farm, for example) or working in the mining industry.

There even have been reports that hands of people who hold a Styrofoam/ polystyrene cup before going through security can test positive.

So skip the lotion, but if you get selected, don’t panic. It’s the unfortunate price of today’s imperfect security.

Q In 1989, my husband had earned enough American Airlines miles for both of us to fly first-class to Hawaii. We weren’t able to use them for many reasons over the years: young children, job losses, health issues. My husband was concerned about the miles expiring, so he got a letter from an American official stating the miles would never expire. However, now we are ready to make the trip — and our miles have expired. We are upset that American has not honored the promise.

A You say 1989? Your miles are the frequent-flier equivalent of holding Civil War bonds.

Although you may have a letter from an official, it is superseded by the rules of the program. Buried in the fine print of all frequent-flier programs is a paragraph that basically says an airline can change the terms and conditions or even shut down its program at any time.

American’s Advantage Miles expire after 18 months unless you have activity on the account. Call customer service at 800-882-8880 and see how much it would cost to get the miles reinstated — if they even have a record of your pre-computerized miles.

The message for all travelers is: Use your miles quickly so they don’t fade away.

Today’s column comes from Ellen Creager of the Detroit Free Press.