How does sun exposure damage our skin?

DEAR DOCTOR K: You've said many times that the sun can harm our skin and increase the risk for skin cancer. How does it do that?

DEAR READER: As you age, the single biggest cause of damage to skin is sun exposure. This damage is called "photoaging." Over the years, sun exposure causes fine and coarse wrinkles; baggy skin with a yellow, leathery appearance; and dry, scaly skin. It also reduces collagen, a natural chemical that gives strength to tissues and that supports a network of blood vessels in the skin. As a result, the skin bruises more easily.

I’m still in pain after a car accident. Why won’t my doctor prescribe more pain medication?

DEAR DOCTOR K: I have been in pain since a car accident a few years ago. My doctor is very conservative in prescribing pain medication. Why not just give me what I need to feel better?

DEAR READER: I don't know the particulars of your case, but I think you are talking about narcotic (opioid) pain medicines. And your doctor probably is reluctant to prescribe opioid medicines for chronic pain -- the kind I assume you now have if your accident was a few years ago.

What can I do to relieve burning mouth syndrome?

DEAR DOCTOR K: For some time, I've had a burning and tingling in my mouth. My dentist and doctor seem to be mystified. What could be causing my symptoms, and what can I do?

DEAR READER: Several things might be causing these bothersome symptoms. Some that come to mind are nutritional deficiencies -- particularly of B vitamins, iron and zinc. These problems can be detected by simple blood tests.

Do I need to get a Pap test every year?

DEAR DOCTOR K: I've had a Pap test every year for 20 years, since I was about 25. It's always normal. Do I still need one every year?

DEAR READER: The answer used to be yes. The reason was that doing the test often would help catch cancer of the cervix at its earliest and most curable stage. However, studies showed that less frequent Pap tests for younger women caught just as many early cancers. The studies also showed that many older women with repeatedly normal Pap smears (like you) had an extremely low risk of ever getting cancer of the cervix.

My father has Alzheimer’s disease. Does that mean my children and I will eventually develop it too?

DEAR DOCTOR K: My father has been diagnosed with Alzheimer's disease. Does that mean that my children and I will eventually develop Alzheimer's too?

DEAR READER: Many people worry that if a parent had Alzheimer's disease, they are doomed. But that's not true. Having a first-degree relative (parent, sibling or child) with Alzheimer's disease increases a person's risk by about 30 percent. That sounds like a lot, and therefore sounds scary. But what you really want to know is: What is my risk in the first place? If it's a very low number, then raising a low risk by 30 percent won't be a big deal.

Why do best practices get reversed so often in medicine?

DEAR READERS: In yesterday's column, I answered a reader's question about why doctors seem to change their minds about the best treatments for medical problems. I said that we doctors keep changing our minds because we're human. We sometimes believe things that seem reasonable and for which there is some evidence. But then we find out, as more and better research is done, that we were wrong.

Why do doctors keep changing their minds about the right thing to do?

DEAR DOCTOR K: I have diabetes, and my doctor used to tell me my fasting blood sugar level needed to be below a certain number. Now, he says it's OK if it's higher. Why do doctors keep changing their minds about the right thing to do?

DEAR READER: We doctors keep changing our minds because we're human. Which means that we sometimes believe things that seem reasonable and for which there is some evidence -- only to find out, as more and better research is done, that we were wrong.

Does the immune system really change with the seasons

DEAR DOCTOR K: A friend heard about a study that said a person's immune system changes with the seasons. That seems incredible to me. But if it's true, it's fascinating. Do you know what she is talking about?

DEAR READER: I think I know the study she is referring to. Before describing what it found, it's worth talking a bit about the immune system and also about genes.

Should I take antioxidants?

DEAR DOCTOR K: It seems like several years ago all my friends were taking antioxidant pills. Now I don't hear about antioxidants as much. Are they worth taking?

DEAR READER: Here's what we know, and here's what is still controversial. The cells of our body are full of chemicals interacting with other chemicals. In the process of getting the energy they need to survive and carry out their functions, cells naturally produce chemicals called "free radicals." Just as political free radicals can sometimes damage society, chemical free radicals can damage body tissues.

What could be causing my painful urination?

DEAR DOCTOR K: I'm a woman in my 50s, and every so often it is painful for several days when I urinate. The doctor tests me, says I don't have a urinary tract infection, and that there's nothing to do. It's true that it goes away, but I'd like some relief when it hurts. Is there anything I can do?

DEAR READER: Urinary tract infections are a common cause of painful urination, but there are other causes as well. And those other causes can be treated. Here's what you need to know before you talk again to your doctor.