Dear Doctor: Is it really that important to walk around during a long flight? I always take a window seat when I fly, and I pretty much stay put because it’s so hard to move around in a plane these days.

Dear Reader: Experts suggest walking around during flights because of the risk of developing a blood clot in the legs, which can be life-threatening. While you’re seated, your legs are bent, and gravity is at work. Over time, your blood flow can become restricted enough to encourage the formation of a blood clot.

When a blood clot forms in the deep veins -- the vessels we can’t see through the skin -- in the lower leg or the thigh, it’s a condition known as deep vein thrombosis, or DVT. And although it’s commonly associated with air travel, deep vein thrombosis is a risk for anyone who stays seated in one position for hours at a time. That includes a flight of about four or more hours, a car trip, a bus ride or even a long session of sitting still at your desk.

Many people who experience deep vein thrombosis won’t even realize it occurred because the clot that formed will dissolve on its own. The risk arises when the clot, or a piece of it, breaks free and travels through the bloodstream. The clot can then become lodged in an artery in the lungs and block the flow of blood, a dangerous condition known as pulmonary embolism. Not only can this result in damage to the lungs, the reduction in oxygen levels can cause harm to organs and tissues throughout the body.

Symptoms of DVT include unusual warmth, swelling, cramping or pain in a thigh, calf, ankle or foot, often on only one side of the body. The pain associated with DVT sometimes may be felt only while moving or walking. There may also be a change in skin color, which can become unusually pale, or perhaps take on a blueish or reddish hue. These symptoms can appear days and even weeks after a clot has formed.

Symptoms of a pulmonary embolism include chest pain that increases while inhaling deeply or while coughing, rapid heart rate, dizziness, sweating, panting and blood in the sputum (saliva). If you have any of these symptoms, seek medical help. A physical exam and simple tests can determine whether a blood clot is the cause.

The good news is that you can take steps to avoid DVT while sitting for extended periods. First, stay hydrated. Drink lots of water, but no alcohol. Wear loose and comfy pants. Avoid crossing your legs at the knee. While sitting, do in-seat exercises, such as wiggling your feet, contracting your calf muscles, and lifting and stretching (as much as you can) your legs. Even better is to stroll up and down the aisle for a few minutes every hour, taking care to consciously stretch your legs and engage the large muscles. We understand that you prefer to stay seated, but DVT is a serious condition, and your health and well-being are at stake.

(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: I was helping with Thanksgiving dinner when the paring knife slipped and sliced my finger. My aunt said to clean the cut with rubbing alcohol, which we didn’t have. I’ve always heard you’re supposed hold it under running water. How do you fix a cut?

Dear Reader: Your aunt isn’t alone in thinking that a cut should be cleaned with rubbing alcohol, but that’s not a good method. Rubbing alcohol is a clear liquid made up of approximately 70% denatured ethanol or isopropanol, and it is used topically in medical settings to clean injection or surgical sites. It’s highly effective due to its chemical properties, which break down the fat-based external membranes of bacteria, killing them. But in these cases, the alcohol is used on skin that is intact. When applied to an open wound, rubbing alcohol can cause tissue damage and actually slow the healing process. This also holds true for hydrogen peroxide, another common go-to disinfectant.

Instead, the best way to clean a cut is to apply a mild soap and hold it under a slow stream of cool or cold running water. Leave it there for at least five minutes. This gently cleanses the wound, and the cool water temperature causes the capillaries to constrict, which helps to slow bleeding. By doing this, you accomplish the first step of caring for a cut -- or any type of wound -- which is to stop the bleeding.

A cut may continue to bleed after you have finished cleaning it. If this happens, apply firm and steady pressure. Be sure that the cloth or gauze you use is completely clean, otherwise you risk reintroducing debris or potentially infectious materials into the wound. If the cut is deep enough and the blood soaks through the cloth or bandage, don’t remove it. You risk dislodging the clot that has begun to form. Instead, add a fresh and clean absorbent layer, and resume applying pressure to the cut.

When the bleeding stops, apply an antibiotic ointment. This helps to prevent infection and to keep the wound moist and lubricated. This last is important to optimal healing, and brings us to another myth about wound care. Despite what you may have heard, you don’t want to “air out” a wound. This encourages the formation of a scab or a crust, which can crack open and become infected. Instead, continue to use the antibiotic ointment, and keep the wound covered with a clean bandage. Once healing has progressed enough that the wound has closed and a scar has formed, continue to keep the area clean and intact.

While it’s safe to treat most minor cuts at home, get professional medical help for cuts with ragged rather than clean edges, when it’s deep enough that bone is visible, and when significant bleeding persists. Any type of puncture wound, which has a high risk of infection, should also be seen by a medical professional. Fever, red streaking, swelling, yellow or green pus, and excessive fluid are signs of infection and require immediate medical care.

(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: I’m 19 years old, and I switched to a vegan diet six months ago. I’m careful about getting enough vitamin B12. However, some of my girlfriends say it’s not that important and your body makes all the B12 you need. Is that true?

Dear Reader: This is a serious issue, and the answer is that nothing your friends are telling you about vitamin B12 is correct. In fact, their advice puts you and any vegans who heed it in real danger. First, vitamin B12 is vital to good health. (More about that in a moment.) And no, your body does not manufacture it. That makes it imperative for everyone following a plant-based diet to make getting adequate B12 a priority.

For those not familiar with the specifics, a vegan diet excludes all animal-based food. That means no meat, fish, seafood, dairy products and eggs. The restrictions also cover honey, which comes from bees, and gelatin, a protein obtained from the bones and connective tissue of animals, often cows or pigs. Because B12 is naturally available only in the major animal products that vegans don’t eat, getting enough becomes a daily goal.

So what is B12 exactly? It’s the most complex of the 12 B vitamins, and it is categorized as an essential vitamin. That means the body requires it, but doesn’t make it. Instead, B12 is produced by certain bacteria that flourish in the gut microbiomes of animals. The B12 they make gets distributed throughout the animal’s body, where it binds to proteins. When you eat an egg, drink some milk or have a burger, the process of digestion releases the B12 from the animal protein and makes it available for your body to use. The vitamin is essential to a wide range of functions involved with the formation of normal red blood cells, the proper functioning of the nervous system and the synthesis of DNA.

A B12 deficiency can result in chronic weakness; mental issues such as poor thinking, confusion or depression; heart palpitations; vision loss; exhaustion; pain and tingling in the extremities; loss of balance; muscle weakness; or difficulty walking. And it’s not just vegans who are at risk. As people age, their digestive systems become less efficient at extracting the nutrient. Those with digestive issues such as Crohn’s disease or celiac disease, immune system disorders such as lupus or Graves’ disease, and those who have had gastrointestinal surgery are also at increased risk of a B12 deficiency.

So how much B12 do we need? For the average teenager and adult, the magic number is 2.4 micrograms a day. Women who are breastfeeding need 2.8 micrograms per day. The vitamin is available to vegans in vitamin supplements; fortified food products such as cereals, some plant milks and brewer’s yeast; and by prescription. The vitamin is not stored in the body, so it’s best to get it daily.

If you’re not sure about your B12 status, your health care provider can check your levels with a simple blood test.

(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.)