Sometimes, when a parent tells me about something that happened with their child, I think (and say, as nicely as I can): Why didn’t they call right away?

And sometimes, when I’m talking to a parent or seeing their child in the office, I think (but don’t say): Why did they call about this?

It can be really hard to know when to call the doctor.

It’s hard because sometimes you plain old don’t know what’s going on. It’s hard because things have a way of evolving, and you can’t always predict whether they are going to get better or worse.

And it’s hard because we don’t want to think that something is really wrong with our child–and at the same time, we don’t want to miss something. Most of us vacillate between denial and overreaction on a regular basis.

So, yeah, it’s hard.

Some things really do warrant a call to the doctor. We’ve made a list (a slide show, even!) of a bunch of them. Although it’s certainly not exhaustive, these are conditions that your doctor really wants to know about right away.

But memorizing a list is tough–and like I said, it’s not exhaustive. So here’s how I’d suggest thinking about it. Call the doctor if:

What is happening is bad. Bad anything. Bad pain. Bad trouble breathing. Bad bleeding. Bad vomiting. I know, bad is subjective. But if in your head the word “bad” seems to apply, better to get advice than wait and watch.

Whatever is happening isn’t going away. Even little things can worry us doctors when they don’t go away. That little limp, the pesky headaches, the rash that the cream isn’t making better, the diarrhea that just doesn’t stop…time to check in.

Your gut is telling you something is wrong. I can’t tell you how much I’ve come to respect and rely on parental instinct over the years. Whenever I hear that from a parent, I want to see that child–and I check them out incredibly carefully. The parents are nearly always right.

You can’t say: I know what to do and really mean it. This takes stopping for a moment and not only really thinking, but really being honest with yourself. Which lots of us don’t do anywhere near as much as we should (both thinking and being honest with ourselves).

None of us knows what to do all the time. That’s true in all spheres of our lives, and parenthood is no exception. We all get stumped and scared; we are all lifelong learners, and that’s okay.

That’s why even though I might wonder why a parent called about something, I wouldn’t dream of chiding them. Instead, I use it as a time to listen, to understand, and to educate. Next time, they’ll know what to do and they won’t need to call.

So read the list–but if what’s going on isn’t on the list and you’re worried, call.

Claire McCarthy is a primary care physician and the medical director of Boston Children’s Hospital’s Martha Eliot Health Center.  She blogs at Thriving, the Boston Children’s Hospital blog, Vector, the Boston Children’s Hospital science and clinical innovation blog, and MD Mama at Boston.com, where this article originally appeared.