People cry to express a range and degree of emotions—from happiness after acing a tough exam to grief after the death of a friend. Some wear their hearts on their sleeves and shed tears at the slightest provocation; others clam up and remain dry-eyed in emotional situations. Crying can even evoke seemingly contradictory behaviors—think “tears of joy.” What provokes this complex behavior in the first place?

Two key factors can help explain why we cry. The first is our crying threshold—the point at which a feeling becomes so intense that we tear up. This threshold varies from person to person. Some have a low threshold and may need only a small push, such as missing the bus to work or being slighted by a friend. But for those with a high threshold, it may take a significant event—the birth of one's child or the loss of a loved one—to produce strong enough emotions. These thresholds may vary throughout a person's lifetime or even within a single day. Being physically exhausted, for instance, can make a person more prone to tears.

The other central factor is the intensity with which an individual reacts to a situation, known as emotional reactivity. Certain people may have their emotional intensity dialed up to 10 most of the time (consider the brooding artist), but such strong feelings will not necessarily bring a person to tears. In other words, whether someone cries depends on how readily he or she responds to a situation, not necessarily the person's baseline emotional state.

It is quite likely that these two elements—threshold and reactivity—interact along a spectrum. At one end, an individual with a high threshold who is thick-skinned may rarely feel the need to cry, whereas on the other end, a person with a low threshold who is hypersensitive may be brought to tears easily.

Interestingly, a tendency to display incongruous behaviors may also influence whether we shed tears. My colleagues and I recently found that someone who expresses feelings dimorphously (in two distinct forms)—such as tears of happiness and of sadness—is more likely to weep in a range of scenarios, regardless of the intensity of the emotion. But we also discovered that incongruous behaviors—such as wanting to pinch a cute baby's cheeks—occur more often when a person feels intensely about something and could help neutralize the extreme feeling.

Overall, crying is not a simple reaction but rather a multifaceted behavior that can offer clues to how we process and regulate our feelings and how we experience the world around us.

Question submitted by Rowena Kong, via e-mail

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