Hello, dear readers, and welcome to the bonus letters column we promised you. We are delighted that you’re keeping our mailboxes full, and we will continue to do our best to stay abreast of your letters.

-- A reader from Oklahoma had a question regarding a takeout dinner that was delivered in Styrofoam containers stacked one on top of the other. “When we got home, the heat from the food in the top container had burned a hole in the top of the bottom one,” he wrote. “We put that container in the freezer, where it still is. Can we safely eat that food?”

Styrofoam is a trademark name for polystyrene, a petroleum-based chemical compound. It’s manufactured from styrene, a volatile colorless liquid. Studies have linked exposure to styrene to genetic damage to white blood cells and to certain blood cancers. Polystyrene is considered safe for food use when in a solid state. However, heating can cause chemicals to leach from the foam and into the food. Eating the contents of a melted foam container one time is unlikely to cause harm. However, repeated exposure, which can be cumulative, can be a health risk.

-- After a column about plantar fasciitis, which occurs when inflammation causes stabbing and often debilitating pain in the heel, a number of readers shared their experiences with this condition. We also heard from an orthopedic surgeon in Nebraska who suggested some treatments that his own patients have found helpful. One is a wearable device known as an Airheel, which uses interconnected air cells to protect and support the foot. Once the inflammation and pain of plantar fasciitis has eased, which can take up to six months, he recommends the use of a rigid plastic heel cup to prevent a recurrence. “The rigidity of the cup helps the fat pad under the heel to maintain its thickness, and thereby absorb the shock at heel strike,” he wrote. He explained that the cup also helps to spread out the impact of each footfall, which lessens pressure on the vulnerable tissues of the heel. We hope readers find this useful.

-- We recently wrote about a link between the repeated concussions and head strikes that are sustained in football and an increased risk of developing amyotrophic lateral sclerosis, or ALS. A reader near Chicago asked if better helmets could protect players from this neurodegenerative disease. “I wonder what effect improved helmets, with more and better padding, would have on the number of players getting ALS,” she wrote. While this seems like a logical solution, more padding itself won’t actually help with brain injuries. A helmet can be effective in protecting against a skull fracture. However, it cannot prevent the brain from being jostled within the skull upon impact. It is this uncontrolled movement of the brain within the skull -- repeatedly injuring and damaging delicate tissues, blood vessels and neurons -- that leads to concussion and other injuries.

Thank you, as always, to everyone who took the time to write to us. We will be back with our regular letters column in a few weeks.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10960 Wilshire Blvd., Suite 1955, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)

Dear Doctors: I think that as I get older, I may be developing a sensitivity to caffeine. If that’s actually something that can happen, it will make me very sad. I have always loved my cup of coffee in the morning, but now I find that it makes me a bit racy. I would love to understand why.

Dear Reader: We join you, along with billions (yes, billions-with-a-b) of people throughout the world in your devotion to caffeine. Whether it’s coffee, tea or other caffeinated beverages, we humans love the lift it gives. Recent data estimate that 85% of adults in the United States consume caffeine in some form each day.

Caffeine stimulates the central nervous system. Due to its physiological effects, as well as its potential for abuse, it is considered a drug. In fact, caffeine withdrawal, which can cause headache, anxiety, insomnia and depression, is a recognized disorder. At the same time, research continues to link coffee and tea, the two most widely consumed caffeinated drinks, to a range of physical and cognitive benefits.

As you have come to suspect, it is indeed possible to develop caffeine sensitivity. Due to certain changes that take place in our bodies as we grow older, this becomes more common as we age. Research shows that older adults clear caffeine from the body more slowly than younger people. In one study, coffee drinkers between the ages of 65 and 70 took 33% longer to metabolize caffeine than did younger participants. A slower clearance rate means the same amount of coffee that someone has been habitually drinking would have an amplified effect. This can cause unpleasant symptoms such as anxiety, irritability, jumpiness, difficulty with sleep, sleeplessness and the “racy” feeling that you describe in your letter.

Caffeine is rapidly and completely absorbed by the body. In fact, within 45 minutes of drinking a cup of coffee, 99% of the caffeine it contains has been absorbed. It makes its way from the digestive tract to the bloodstream, where it can reach peak levels within 15 minutes of consumption.

After a few hours, certain enzymes in the liver begin to metabolize, or break down, the caffeine. This occurs gradually, and in a series of steps. In a healthy young adult, it takes about six hours for the liver to cut the amount of circulating caffeine in half. But as people age, the enzymes involved in caffeine metabolism grow less efficient. This leads to the slower clearance rate that we discussed earlier. Other factors, such as pregnancy, certain medications and being a smoker can also slow the rate at which caffeine is metabolized.

When someone becomes sensitive to caffeine, it can become necessary to rethink consumption in order to avoid the adverse effects. An 8-ounce cup of coffee delivers between 80 and 100 milligrams of caffeine. Research shows that for older adults, amounts in the range of 50 to 100 mg are well-tolerated. To manage caffeine sensitivity, try limiting yourself to one cup a day. And if multiple cups are your routine, consider switching to a half-caf blend.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10960 Wilshire Blvd., Suite 1955, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)

Dear Doctors: How on Earth did my son get pinworms? I didn’t even realize something was wrong until he started scratching his butt in his sleep. The minute we told his pediatrician about the scratching, she suspected pinworms. Does this mean the rest of the family has been exposed?

Dear Reader: Pinworm is the common name for a small, pale roundworm known as Enterobius vermicularis. They are also sometimes called threadworms due to their slender, threadlike appearance. These tiny parasites, which are about the length of a staple, are the most common cause of worm infections in the United States.

Pinworms live in the colon and the rectum of humans, who are their sole hosts. Pinworms do not live in animals. In order to lay eggs, a female pinworm travels from the colon to the tissues of the anus. This typically happens at night. It often results in intense itching that can wake someone from sleep. That’s the symptom that led your son’s pediatrician to suspect a pinworm infection. The reassuring news is that while pinworms are a little gross, certainly annoying and perhaps embarrassing, they are easily treated and seldom cause serious health problems.

It’s possible but rare for pinworms to travel from the anus to the vagina. This is typically associated with heavy infestations that go untreated and can lead to a urinary tract infection, and also possibly affect the pelvic organs.

A pinworm carrier can easily spread the infection. Whenever an infected person fails to thoroughly wash their hands after using the bathroom or scratching their anus, they can transfer microscopic eggs to any surfaces that they touch. When someone touches that surface, and then later touches their mouth, they can become infected. The eggs travel through the digestive tract to the colon. Once there, they hatch and, within a few weeks, grow into mature worms.

Diagnosis is made by identifying the worm or its eggs. Worms may be visible on the skin near the anus a few hours after falling asleep. Sticky tape can be used to collect eggs from the anus in the morning, and then given to your doctor to be examined.

Although anyone can become infected with pinworms, it’s most common in children younger than 10 years old. Kids that age often have their fingers in their mouths, and they aren’t always great about washing their hands. Schools, preschools and day care centers are common sources of pinworm infection. You asked if your son’s infection means your family has been exposed, and the answer is that it’s quite likely. Anyone living with or caring for an individual with pinworms is at risk of infection.

To stop the cycle of infection, it is recommended to treat everyone who may have been exposed. This may consist of a single dose of an over-the-counter medication known as pyrantel pamoate, which paralyzes the worms and allows the body to safely remove them via the stool. Although available without a prescription, we strongly recommend that this medication be used under medical supervision. Several prescription anti-parasite medications are also extremely effective. Anyone who suspects a pinworm infection should see their health care provider for diagnosis and treatment.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10960 Wilshire Blvd., Suite 1955, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)