Motor tics like the one you describe may affect as many as 25 percent of children at some point. The movements, such as grimacing, shrugging, blinking, or head shaking, are involuntary; the child can control them briefly, but doing so is very uncomfortable and difficult. We don't entirely understand what causes them, though we do know the triggers are different for every child (stress is a common one). That said, we don't usually worry about an underlying medical cause unless: the movements seem more like seizures; they come on very suddenly and happen very frequently; the child is taking a medication, especially a stimulant; or the child has an ongoing or recent strep infection. If any of this is true, or if the head shaking is interfering with daily life, see your M.D. Medication may be needed to control the behaviors. The good news is that the majority of tics in children go away by themselves, usually within a year or so.

Pediatrician Claire McCarthy, M.D., is medical director of the Martha Eliot Health Center in Boston. Send her your health questions at Meet the Mom Squad.

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