Editor's note: Aaron E. Carroll and Rachel C. Vreeman are pediatricians and health services researchers at the Indiana University School of Medicine. They are also the authors of "Don't Cross Your Eyes... They'll Get Stuck That Way!", recently published by St. Martin's Press.

(CNN) -- You might not be a doctor, but we bet you think you know exactly what to do if you scrape your knee.

First, you might use hydrogen peroxide to clean the wound. Second, you might leave it uncovered at night so it can air out and heal faster. Finally, you might apply some vitamin E cream if you want to prevent an unsightly scar. As pediatricians, we might have recommended the very same steps to care for your child's wounded knee.

But, all of us would have been wrong. Wrong about hydrogen peroxide, wrong about uncovering the wound and wrong about vitamin E.

Now, the ideas behind these steps make sense. Hydrogen peroxide looks like it's working as it bubbles and stings. An uncovered cut seems to dry up, scab and look less moist and open.

But multiple randomized, controlled trials -- the best kind of research -- show that hydrogen peroxide does not prevent or treat infections in wounds. Not only that, hydrogen peroxide slows healing and may even cause cellular damage. That bubbling you see? It's probably the hydrogen peroxide attacking you.

Uncovering your wound at night? It's actually one of the last things you want to do. Careful studies reveal a moist, covered environment is best for wound healing. And most studies of vitamin E show no improvement whatsoever in the size, thickness or appearance of scars after using it. Moreover, many people get an itchy rash from using vitamin E.

Now, these examples are unlikely to cause serious harm, but doctors sometimes believe and recommend more serious treatments that could.

For example, if your snot turns green, many physicians take that as a sign that you need an antibiotic -- even though research shows that green mucus does not make you any more likely to need an antibiotic. And, not only might you have a bad side effect or allergic reaction to that unnecessary medication, but these unnecessary prescriptions might contribute to our problems with antibiotic-resistant bacteria.

Why do we believe these things that are just not true? Often, it's because they have a grain of truth in them.

Cold weather does not make you sick, but, in the United States, the peak in certain cold and flu viruses comes during winter. Other ideas just seem reasonable.

It seems like sit-ups should flatten your stomach (although they don't, really) or that the toilet seat must be the dirtiest thing in the bathroom. And sometimes, we have heard these myths enough times, or from people we trust, that they become ingrained. You've heard them from your parents, your teachers or even your doctors, so they must be true.

While some medical myths can be fun to examine, the consequences of others can be serious. When myths stop us from getting our children vaccinated, getting ourselves flu shots or taking medications appropriately, they are dangerous.

The important question for medical practice, health policy decisions and scientific inquiry in general is this: Can the evidence conquer our beliefs?

When we talk about "evidence-based medicine," people often focus on new studies to determine whether approaches work or don't. Certainly, practicing good care does require the constant acquisition of new knowledge. And, we rely heavily on new scientific research to guide our understanding of what medical practices are or aren't effective.

Physicians, however, too often assume that the medical ideas we already have do not need re-examination. We don't want to hold our previously held beliefs up to evidence. All of us, including doctors, need to examine the evidence supporting our medical decision-making, recognizing where practice is based on tradition, anecdote or art, as opposed to science.

We researched 76 commonly held beliefs about our health and bodies, using stringent research skills. We found many of these ideas, even those doctors believe, are just plain wrong. Evidence disproves these myths over and over again.

Artificial sweeteners will not give you cancer. Cheese is not going to constipate you. Stretching before you run might not be a good idea. Eggs do not give you high cholesterol. And even the cold weather is not going to make you sick.

These reminders about all the ways we can be wrong -- even in how we treat our scraped knees -- also can remind us that we need to question what other medical falsehoods we unwittingly support. All of us, including physicians, need to examine the evidence supporting our medical decisions, recognizing where practice is based on tradition, anecdote or art, as opposed to science.

We like to think that we are always right. Discovering that something you believed is not true can be disturbing and unsettling. Science is all about comparing a belief with the evidence -- that's what we call testing a hypothesis. And when you test hypotheses, sometimes you discover that the hypothesis is wrong. But the testing is a crucial step.

Maybe as we learn to hold our beliefs up to the evidence again and again, we will become more comfortable using evidence to direct future treatments, guidelines and policies.

The opinions expressed in this commentary are solely those of the writers.