Take the anxious parents who came into my office recently with their 2-month-old. "It's her right eye," her mom said. "It's different from the left one. We looked it up on the Internet, and we think she has ptosis!" Ptosis, or a droopy eyelid, can be associated with nerve and brain problems  -- something I'd never suspected this baby of having. Had I missed something? I looked her over carefully. "She doesn't have ptosis," I told them. "Her eyes just aren't symmetrical, and that's totally normal."

But I couldn't convince them. They decided to consult with an ophthalmologist, who confirmed that the baby was fine. Their foray onto the Internet had cost them weeks of angst and a pricey specialist visit  -- all unnecessary.

I'm not saying the web can't be a great resource  -- it can be. I can't always spend as much time as I'd like explaining things to patients; a good site can help with that, and answer questions that come up after they leave my office.

There's also a lot of useful health and safety information on the web, from the most up-to-date car-seat installation recommendations and toy recalls to food-allergy information you can print out and give to your daycare provider and tips on getting lice out of hair. Online message boards and disease-support websites can be invaluable when it comes to connecting families who are going through the same health crises.

But as a doctor, I know how to pick out the reliable info from what's untrue. Without medical training, that's hard to do. And there's enough misinformation out there to drive you crazy. Here's what to know so you can surf safely and effectively.

Don't use the Internet to diagnose yourself or your child.
That's what doctors study and practice for years to be able to do. If you have concerns about your child, call your pediatrician first.

I understand the temptation to Google a symptom or to take one of those online health quizzes; it's easy, and unlike your doctor, the Internet's always available (and you never have to worry about waking it up). But there are two problems:

The Internet can't examine your child. Let's say your baby's breathing sounds a little funny. What do you enter into that search engine: "wheezing" or "nasal congestion"? Your results will be really different depending on which you pick-and both could lead you down scary roads that may have nothing to do with your kid's problem. Without a doctor to check out your child, it's hard to say whether she has congestion or wheezing (or croup or pneumonia).

The Internet can't take a history, which is what doctors do when we ask questions to understand what's going on. Say your son has been having headaches. Type "headache" into Google and a dizzying array of sites come up, with an even more dizzying range of possible causes, from tension to a brain tumor(!)  -- without much to help you sort them out.

Contributing editor Claire McCarthy, M.D., writes our On Call column.

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