Dear Doctor: I’ve tried all the toenail fungus cures in our drug store, and so far nothing works. Why not? What can I do? I really miss wearing sandals.

Dear Reader: You are one of the estimated 6 million people in the United States struggling with toenail fungus. It’s not only common, but, as you’ve learned, it’s a challenge as well. That’s because, although the symptoms affect the visible part of the toenail, the fungi causing the infection actually live underneath the toenail.

Toenail fungus is usually caused by one of a group of microscopic organisms called dermatophytes. Like the yeasts and molds they’re related to, these fungi absorb nutrients from organic substances. In the case of toenail fungus, the food source is the portion of the toenail known as the matrix. It’s found at the base of the nail, beneath the cuticle. The matrix is served by a network of nerves and blood vessels, and it generates the cells that become the new growth of the toenail. Although this type of fungal infection can affect the fingernails as well, it’s more common in the toenails due to the warm, moist and dark environment provided by socks and shoes.

A fungal infection in the toenails typically begins with discoloration, often in a brown or yellowish hue. As the nail grows, it may become thick, malformed and crumbly. The infection is hard to treat due to the makeup of the nail, which is a tough, close-knit protein known as keratin. Some of the topical creams and liquids available at your local drug store can make the nail look better. However, keratin isn’t porous, so even medications that advertise themselves as antifungal can’t reach the infection. Even as your nails protect your tender toes, they shield the infection. The success rate of these types of medications is quite low.

Many people have good results with systemic medications, which are available by prescription. You take a pill, your digestive system releases the medication and your circulatory system delivers it to that network of blood vessels in the nail matrix that we discussed earlier. These types of meds can have side effects, which range from headache and stomachache to liver damage. When taking a systemic antifungal, it’s important to monitor liver function via regular blood tests. Nail growth is slow, which means treatment is a lengthy process. Oral treatment for toenail fungus typically takes three or four months, but it can take a year or more for toenails to look normal again.

Newer treatments for toenail fungus include a prescription topical liquid and laser treatment. Each of these approaches have had mixed results. We’ve discussed toenail fungus here before, and we have heard from many readers about their own preferred home remedies. These include daubing the affected nails with Vicks VapoRub and with tea tree oil. Clinical trials have shown that these novel treatments, while not a complete cure, may have a positive effect. We recommend that you check with your family doctor about which treatment would be best for you.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10880 Wilshire Blvd., Suite 1450, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)

Dear Doctor: What can you recommend for motion sickness? We’ve been taking the family driving a lot lately to get us out of the house, but unless I’m the one behind the wheel, the mountain roads where we live make me nauseated.

Dear Reader: There’s nothing like a bout of motion sickness to ruin an otherwise fun day. The symptoms can range from the queasy stomach that you describe to dizziness, a throbbing headache, cold sweats, anxiety and vomiting. It’s a common affliction, and we wouldn’t be surprised if the other passengers in your car aren’t suffering a bit as well.

Although the exact cause of motion sickness remains unclear, it appears to be linked to a miscommunication between what our eyes are telling us and what is being reported by the delicate structures of the inner ear. Known as the vestibular system, this is the mechanism that controls balance. When you turn your head, bend down or twist around, the resulting image you’re seeing is in sync with what your inner ear says is happening. Your physical body is in motion, but the ground is stationary. In a car on a twisty road, however, the signals get mixed. Your eyes say your body is sitting still, but to your inner ear, your body is in motion. It’s not clear how or why, but this sensory dissonance stimulates pathways in the brain that lead to the often gut-churning symptoms of motion sickness. For whatever reason, the brain has decided the body is best off purging itself, and either nausea or vomiting can be the outcomes.

For some people, medications that address the symptoms of motion sickness can be helpful. This includes over-the-counter products with dimenhydrinate, an antihistamine used to control nausea and vomiting, or meclizine hydrochloride, an antiemetic to prevent nausea, vomiting or dizziness associated with motion sickness. Take it an hour or two before you head out. If over-the-counter meds aren’t working, consider prescription medications such as the scopolamine patch and promethazine. These are also useful for symptoms of seasickness. Dimenhydrinate and meclizine hydrochloride can cause dry mouth and drowsiness. If you choose a prescription remedy, be sure to go over the potential side effects with your pharmacist.

Since you know you’re prone to motion sickness, you can take precautions before the drive. Avoid a heavy meal before you head out. Stay hydrated, but skip the caffeine, beer or cocktails. Crack a window to get a steady supply of fresh air. Opt for the front seat, where you can easily keep your eyes on a fixed point on the horizon in front of you. That helps your brain unscramble the mixed signals sent by your eyes and inner ear. Some travelers swear by ginger, available in powdered form, to ease nausea. Despite conflicting evidence about its efficacy in easing motion sickness, acupressure also has its proponents. In this method, constant pressure is applied to the insides of the wrists via specially designed elastic wristbands.

If all else fails, consider taking a turn behind the wheel. It’s not known why, but having control over the car sharply reduces the risk of motion sickness.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10880 Wilshire Blvd., Suite 1450, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)

Dear Doctor: Why do I sneeze after a meal? It doesn’t matter what kind of food it is, and it doesn’t have to be after a particularly big meal. Beverages don’t seem to be an issue. What’s going on?

Dear Reader: You’ve described a condition known as gustatory rhinitis. When something irritates the mucous membranes of the nose and causes them to become inflamed or swollen, it’s known as rhinitis. It can result in nasal congestion that ranges from mild to severe, a runny nose, postnasal drip and sneezing. Rhinitis is divided into two categories: allergic and non-allergic. Gustatory rhinitis falls into the latter category. Although the symptoms are similar to those of an allergy such as hay fever, the condition doesn’t involve the same type of immune response.

We tend to think of sneezing as a reaction to inhaling an irritant that “tickles” the nose, such as pollen, dust, pet dander, perfumes, mold, pollutants or smoke. The purpose of the propulsive gust of air delivered by a sneeze is to clear away that irritant. However, sneezing has other triggers. Some people sneeze in response to cold air, fizzy drinks, pungent foods such as chili or peppermint, sexual activity, exercise, when plucking an eyebrow, or when emerging from dim light and then looking at the sun or other bright light. Interestingly, sneezing associated with bright light, known as photic sneeze reflex, occurs in 20% to 35% of the populace and has been linked to genetics. Individuals who have this response often sneeze the same number of times in each episode.

People who sneeze when their eyebrows are plucked are responding to stimulus to the trigeminal nerve, one of the 12 cranial nerves. It has three separate branches, which send sensations from the upper, middle and lower portions of the face to the brain. When the branch of the trigeminal nerve in the forehead is stimulated by tweezing, threading or waxing an eyebrow, the branch of the nerve in the nasal area is activated as well, which can result in a sneeze.

When it comes to the type of gustatory rhinitis you’re experiencing, which some people refer to as “sneezures,” the mechanism isn’t fully understood. In some cases, post-meal sneezing arises as the result of spicy or pungent foods. Common triggers can include horseradish, peppercorns, hot peppers, pickled foods, wasabi and dark chocolate. Temperature can also play a role. For some people, a sip of hot soup can bring on a sneeze. Sneezing at the end of a meal also has been linked to the stomach becoming full and, thus, distended. There is evidence that this, too, has a genetic component. Gustatory rhinitis also becomes more common as people age.

Although not a health risk, sneezing after a meal can be an unpleasant distraction. It’s a good idea to monitor what you’re eating just to rule out a link to the contents of the meal. A pattern you hadn’t noticed before may emerge. It’s also possible that eating smaller meals, which don’t distend the stomach as much, may also bring relief.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10880 Wilshire Blvd., Suite 1450, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)