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.)

Dear Doctors: Can you please talk about myasthenia gravis? Our oldest daughter has been diagnosed with it. She’s 33 and lives with her family in another state, but we want to understand what she’s dealing with. I just read about Chinese herbs that can be helpful. Do you know if that’s true?

Dear Reader: Myasthenia gravis is a long-term disease that adversely affects the skeletal muscles. These are the muscles that, with the help of tendons and ligaments, make it possible for the body to move and perform a wide range of functions.

Skeletal muscles are known as voluntary muscles, which means they are under a person’s direct control. Myasthenia gravis does not affect the involuntary muscles, such as the heart, or those that line the blood vessels, organs, stomach and intestines. When someone has myasthenia gravis, their skeletal muscles become weak and quickly grow fatigued when in use.

The name of the disease is drawn from Greek and Latin and means grave or serious muscle weakness. The condition is caused by a glitch in the immune system that mistakenly blocks the pathways of communication between the muscles and the nerves that animate them. Taken together, and in more scientific terms, myasthenia gravis is a chronic neuromuscular autoimmune disease.

Symptoms include drooping eyelids, weakness in the eye muscles, difficulty swallowing, impaired speech, difficulty breathing, and weakness in the neck, arms, hands, fingers or legs. Since each case is different, symptoms vary in type and intensity. Some individuals have mild disease in which treatment isn’t necessary. In severe cases, weakness in the muscles of the chest and diaphragm impairs the ability to breathe effectively. This is known as myasthenic crisis, and it is a medical emergency.

The disease can occur at any age, but it is more frequently seen in young women in their 20s and 30s and men aged 50 and older. There is no cure for myasthenia gravis at this time. Treatment focuses on improving muscle function and preventing problems with swallowing and breathing. This can include the use of steroids, immunoglobulin or monoclonal antibodies, each of which modulate immune response. The thymus, a small gland located in the upper part of the chest between the lungs, appears to play a role in the disease. Surgical removal of the thymus can sometimes lessen the need for medication and prevent more severe symptoms.

As to your question about Chinese herbs, we think you are referring to a small study that was recently reported in the news. The results, published in the medical journal Frontiers in Neurology, found that a blend of herbs used in traditional Chinese medicine, known as Fufang Huangqi Decoction, can have a beneficial effect on certain imbalances common to the gut microbiomes of people with myasthenia gravis. This echoes the findings of previous studies.

While this research suggests the potential benefits of new treatment pathways, it’s important to note the studies only looked at the effects of the herbs on the gut microbes of people living with myasthenia gravis. They did not explore their effect, good or ill, on the patients themselves and made no recommendations regarding their use.

(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.)