THERE are plenty of reasons to put our cellphones down now and then, not least the fact that incessantly checking them takes us out of the present moment and disrupts family dinners around the globe. But here’s one you might not have considered: Smartphones are ruining our posture. And bad posture doesn’t just mean a stiff neck. It can hurt us in insidious psychological ways.

If you’re in a public place, look around: How many people are hunching over a phone? Technology is transforming how we hold ourselves, contorting our bodies into what the New Zealand physiotherapist Steve August calls the iHunch. I’ve also heard people call it text neck, and in my work I sometimes refer to it as iPosture.

The average head weighs about 10 to 12 pounds. When we bend our necks forward 60 degrees, as we do to use our phones, the effective stress on our neck increases to 60 pounds — the weight of about five gallons of paint. When Mr. August started treating patients more than 30 years ago, he says he saw plenty of “dowagers’ humps, where the upper back had frozen into a forward curve, in grandmothers and great-grandmothers.” Now he says he’s seeing the same stoop in teenagers.

When we’re sad, we slouch. We also slouch when we feel scared or powerless. Studies have shown that people with clinical depression adopt a posture that eerily resembles the iHunch. One, published in 2010 in the official journal of the Brazilian Psychiatric Association, found that depressed patients were more likely to stand with their necks bent forward, shoulders collapsed and arms drawn in toward the body.

Posture and Emotional State

Posture doesn’t just reflect our emotional states; it can also cause them. In a study published in Health Psychology earlier this year, Shwetha Nair and her colleagues assigned non-depressed participants to sit in an upright or slouched posture and then had them answer a mock job-interview question, a well-established experimental stress inducer, followed by a series of questionnaires. Compared with upright sitters, the slouchers reported significantly lower self-esteem and mood, and much greater fear. Posture affected even the contents of their interview answers: Linguistic analyses revealed that slouchers were much more negative in what they had to say. The researchers concluded, “Sitting upright may be a simple behavioral strategy to help build resilience to stress.”

Slouching can also affect our memory: In a study published last year in Clinical Psychology and Psychotherapy of people with clinical depression, participants were randomly assigned to sit in either a slouched or an upright position and then presented with a list of positive and negative words. When they were later asked to recall those words, the slouchers showed a negative recall bias (remembering the bad stuff more than the good stuff), while those who sat upright showed no such bias. And in a 2009 study of Japanese schoolchildren, those who were trained to sit with upright posture were more productive than their classmates in writing assignments.

How else might iHunching influence our feelings and behaviors? My colleague Maarten W. Bos and I have done preliminary research on this. We randomly assigned participants to interact for five minutes with one of four electronic devices that varied in size: a smartphone, a tablet, a laptop and a desktop computer. We then looked at how long subjects would wait to ask the experimenter whether they could leave, after the study had clearly concluded. We found that the size of the device significantly affected whether subjects felt comfortable seeking out the experimenter, suggesting that the slouchy, collapsed position we take when using our phones actually makes us less assertive — less likely to stand up for ourselves when the situation calls for it.

Smaller Phones Are Worse

In fact, there appears to be a linear relationship between the size of your device and the extent to which it affects you: the smaller the device, the more you must contract your body to use it, and the more shrunken and inward your posture, the more submissive you are likely to become.

Actually design a device around the human body and to be ergonomic in the first place, instead of changing the designs…

Despite all this, we rely on our mobile devices far too much to give them up, and that’s not going to change anytime soon. Fortunately, there are ways to fight the iHunch.

Keep your head up and shoulders back when looking at your phone, even if that means holding it at eye level. You can also try stretching and massaging the two muscle groups that are involved in the iHunch — those between the shoulder blades and the ones along the sides of the neck. This helps reduce scarring and restores elasticity.

Finally, the next time you reach for your phone, remember that it induces slouching, and slouching changes your mood, your memory and even your behavior. Your physical posture sculpts your psychological posture, and could be the key to a happier mood and greater self-confidence.

Amy Cuddy is a professor at Harvard Business School and the author of the forthcoming book “Presence: Bringing Your Boldest Self to Your Biggest Challenges.”