Dear Doctor: My hair has been thin since I was young, and now that I’m growing older, it’s getting worse. Why is that happening? Is there anything I can add to my diet to make my hair thicker and healthier, or is thinner hair inevitable with aging?

Dear Reader: Among the many changes we can expect to see in our bodies as we grow older are gradual differences in the appearance of our hair. In addition to going gray and, for some people, growing bald, this includes changes to hair’s thickness and texture. Aging hair typically grows more slowly and becomes more sparsely distributed. The strands themselves become more brittle, dull and thinner than they had been in the past. They become more fragile, as well, which can lead to increased splitting and breakage. Since the state of our hair contributes to our overall appearance, as well as to our sense of self, it’s understandable that these changes might be unwelcome.

A single strand of hair is composed of three separate layers of a hard protein called keratin. In younger adults, it has a life span of two to seven years -- or more -- and grows about one-half inch per month. Due, in part, to hormonal changes as we age, hair falls out more quickly in older adults and is replaced with finer hair that grows more slowly. Some hair follicles go completely dormant. Genetic, environmental and behavioral factors can also play a role in these changes and vary greatly from person to person. The good news is that, although you can’t completely turn back the clock to youthful hair, there are steps you can take to navigate these changes.

You asked about diet, and you’re correct that it can make a difference. The cells in hair follicles have a high rate of turnover, so maintaining a balanced diet is important. Some studies have suggested that supplementation of biotin, one of the B family of vitamins, can contribute to healthier hair. However, the National Institutes of Health reports there is insufficient data to back up these claims. Added biotin in the diet can interfere with important medical test results, including those used to diagnose heart problems, and can interact with some medications. Better to focus on getting adequate protein in your diet and eating from a wide range of fresh fruits and vegetables for vitamins and minerals.

Because hair becomes more fragile as we age, you’ll want to examine your styling routine, including the use of hair dryers and curling irons. Although it’s tempting to use hair sprays to build up volume, the alcohols they contain can contribute to drying. Try to find a good hydrating shampoo and conditioner to help your hair stay strong and flexible.

Certain medications, including some that control blood pressure and manage blood cholesterol, can contribute to thinning. Your doctor can let you know if this is the case and help find a solution. Some women opt for medications that promote hair growth, such as Rogaine or Propecia. Again, whether or not to go this route is a discussion you should have with your health care provider.

(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 am 53 and have diabetes. I live in California and can get the COVID-19 vaccination soon. What side effects can I expect? There are so many stories floating around, and knowing what to believe is hard.

Dear Reader: It’s true there’s a lot of confusion and, sadly, misinformation about the coronavirus vaccine. We’ve been answering specific questions in recent columns, and we are happy to share the bigger picture with you and the rest of our readers.

At this time, three vaccines have received emergency authorization from the U.S. Food and Drug Administration. They are manufactured by Pfizer, Moderna and, most recently, Johnson & Johnson. Clinical trials found all three vaccines to be effective in preventing symptomatic COVID-19. The Pfizer and Moderna vaccines require two doses, with the second dose administered three or more weeks after the first. The exact interval depends on which vaccine you receive; you get directions about how and when to get your second dose at the time you receive your first. Johnson & Johnson’s is a single-dose vaccine.

Potential side effects from the coronavirus vaccine can range from mild to severe. Anaphylaxis, which is a life-threatening allergic reaction, has received a lot of attention. However, this response to the vaccine is exceedingly rare. According to the latest figures from the Centers for Disease Control and Prevention, which tracks a wide range of data related to the vaccine, we are currently seeing about 2.5 episodes of anaphylaxis for every million doses of COVID-19 vaccine doses administered.

The vaccine itself is delivered via a very thin needle. Many people say they don’t even feel the injection. After you receive the vaccine, you will be directed to a designated area to wait during the CDC-mandated 15-minute period before leaving the site. People at risk of an allergic reaction, which is determined via a pre-vaccination questionnaire, are asked to wait for at least 30 minutes. Each vaccine site is required to have on hand the medication, equipment and trained medical personnel needed to address potential serious allergic reactions.

The most common side effect of the vaccine is temporary soreness and swelling at the injection site. This can begin anywhere from a few minutes to a few hours after the injection. Additional reactions can include fever, chills, headache, muscle aches, nausea and fatigue. These arise because the vaccine delivers a fragment of the coronavirus’s genetic code to stimulate the immune system to recognize it as a foreign invader and mount a response. You can reduce potential discomfort at the injection site by exercising your arm prior to getting the vaccine, and by applying a cool, wet cloth to the injection site.

Some people have a stronger response to the second shot of the two-dose vaccines. If that’s the case, over-the-counter meds such as aspirin, acetaminophen or ibuprofen can help manage post-vaccination symptoms. But don’t take these meds ahead of time to prevent side effects, as it’s not yet known if they affect the vaccine’s efficacy. If symptoms don’t go away after a few days, or if they grow worse, be sure to see your health care provider.

(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.)

Hello again, dear readers, and welcome to part two of our letters column about the COVID-19 vaccine. We continue to get questions about this topic and, because it’s so important, will continue to address them as quickly as possible.

-- Many of you are wondering if blood thinners, both prescription and over-the-counter, affect the coronavirus vaccine’s efficacy, and vice versa. It’s a question we’re getting from our own patients. The guidance at this time is to continue with blood thinners as prescribed, and to tell the person administering the vaccine that you are using them.

-- A reader who works in a hospital setting had a question related to Parkinson’s disease. “I’m a 71-year-old female who works part-time in a hospital, and I interact with staff and clinical equipment,” she wrote. “I have a strong family history of Parkinson’s disease and am concerned that the mRNA might have an unknown trigger effect for Parkinson’s disease.” There is no data at this time to support the idea that mRNA vaccines trigger Parkinson’s disease. However, we understand why this is a concern for you. We recommend discussing the issue with your family doctor, who can help guide your decision regarding the vaccine.

-- We heard from a daughter whose 72-year-old mother is eligible for the vaccine. “My mother was diagnosed with shingles this past January and is taking her medical treatment,” she wrote. “Do we need to wait for her to get the COVID-19 vaccine, or can she get it now?” The Centers for Disease Control and Prevention advises that no other vaccines be given within 14 days of getting the COVID-19 vaccine. However, there is no contraindication to receiving the COVID vaccine while taking shingles medication.

-- People who become infected with the coronavirus are often unsure exactly when it happened. A reader who recently lost her brother to COVID-19 has been left with this question. A cluster of infections spread through her brother’s small business over the course of 27 days, with a receptionist never becoming ill. “Could the receptionist have been asymptomatic?” she asked. “How long can an asymptomatic person transmit the virus?” A year into the pandemic, we know that the incubation for COVID-19 is between two and 14 days, hence the two-week quarantine recommendation. If the final person became ill 27 days after the first illness, then the receptionist could not have been the source of exposure for all of the infections.

-- Many people are concerned about allergic reactions to the vaccine. “I am an active 80-year-old and happen to be extremely allergic to bees and ants, and I carry an EpiPen,” a reader wrote. “I am wondering if I should receive the vaccination under a hospital setting?” Each vaccination site is required to have on hand the medicine and equipment to deal with adverse reactions to the vaccine. All patients are asked about their allergy status, and they are monitored for at least 15 minutes after receiving the vaccine. Be sure to disclose your allergy at your vaccination appointment, and speak up immediately if you begin to feel ill.

(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.)