With temperatures forecast to reach around 37°C in places, reaching for an ice cream or an icy drink might seem like an excellent idea. There is, however, one small hazard to eating your frozen treat with too much enthusiasm: brain freeze.

That sudden, stabbing pain is officially classified as a cold-stimulus headache. The International Headache Society describes it as a headache caused by eating, drinking or inhaling something very cold. “Ice-cream headache” and “brain freeze” are much easier to say while clutching your forehead.

And it is surprisingly common. In one study of 618 people aged 17 to 63, just over half said they had experienced brain freeze.

Scientists still do not know exactly what causes it, partly because a headache that disappears almost as quickly as it arrives is difficult to study.

Very cold food or drink touching the roof of the mouth or the back of the throat can trigger the pain. One important player seems to be the trigeminal nerve, a large nerve that carries information about sensations, including pain and temperature, from the face and parts of the mouth to the brain.

When the roof of the mouth is suddenly chilled, researchers think the cold activates pathways involving this nerve. That may help explain one of the strangest things about brain freeze. The cold........

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