"My teen can be so irritable! Is that normal?" This ranks high on the list of parental concerns I encounter as a child psychologist.

In response, I often raise my eyebrows and shrug. Translation: is anything "normal" during adolescence?

Or I offer the (equally unsatisfying) answer: "Your teen is irritable because she has an anxiety disorder, is depressed, or only eats a total of six things. And that's not normal. It's why she's in my office in the first place."

But outside of my office – out in the "real world," as I like to call it – just how normal is irritability among the general population of adolescents?

The answer, according to a strong study published online last month in Journal of the American Academy of Child and Adolescent Psychiatry, is that irritability is pretty common, but not necessarily normal.

Let me explain.

The study was strong because of the quality of the data used from the Great Smoky Mountains Study. In the very well-designed research, 1,400 9-13 year olds, recruited from their communities in western North Carolina, were interviewed about their psychological health each year until the age of 16.  Their parents were also interviewed every year, which is important, because it meant researchers had two sources of information from which to draw their conclusions.

The interviews were comprehensive and concerned the what, when, how long, and how much of psychological disorders and related problems.

What were the results when it came to tween and teen irritability?

First, parents of middle-schoolers take heart: As the tweens aged into teens, their irritability tended to decline. This is perhaps not surprising (but certainly welcome), given that the ability to self-regulate one's emotions and behavior increases as the brain matures.

Second, irritability was found in almost equal rates among females and males. Surprised? You thought it would be girls, right? So did the five random adults I just asked (all of whom told me that they had children of both genders). But in this study, gender didn't matter. At every age from 9 to 16, both girls and boys were reported to experience about equal irritability.

Third, the experience of irritability wasn't rare. In fact, at any given point during the study, 51 percent of the adolescents had experienced a temper tantrum or anger outburst within the last three months and 28 percent had a longer period of feeling easily annoyed or touchy.

So irritability among 9-16 year olds is indeed common.

But normal?

This is where things get tricky.

The results also showed that any report of irritability, at any age, made it more likely that the child was also experiencing other problems. This was the case even when the level of reported irritability was low.

In this study, problems associated with irritability included family report that the child's symptoms were a problem and the child needed help, school suspensions, symptoms of anxiety and depression, and use of mental health services.

Remember: The above result does not mean that all children who experienced irritability had these problems, just that they were more likely to have them than children without reported irritability.

What should parents make of these results? William Copeland, PhD, lead author of the study and a clinical psychologist and epidemiologist from Duke University Medical Center, had this to say: "Most kids with low levels [of irritability] will be fine. I think the message is to not disregard low levels of irritability as unimportant, but to use that as a signal to be more vigilant about the child's functioning. Talk to the child about it, keep an eye on them, and generally be on the lookout for other signs that may indicate the child is struggling."

In other words, irritability among tweens and teens may be common, but might also hint at more serious concerns.

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