By Greg Argos

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PHILADELPHIA (CBS) — Hold the phone — your smartphone could be hurting you all because of how you hold it.

What costs hundreds, is used by millions and is touched by its users, at least according to one study, 5,400 times a day? We’re talking about your smartphone.

And it could be causing some serious damage to your hands and wrists.

“From the time I wake up, throughout the day, until I go to bed,” one woman said.

“I use it to check the time, check emails, check messages,” said one man.

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“What we’re seeing quite a bit is the problems with the thumb and the tendons crossing the thumb and wrists,” said Joe Zarett, owner of a physical therapy clinic that bears his name.

He’s seen an increase in customers coming in for treatment of their hands and thumbs from cellphone overuse — known by some as “smartphone thumb.”

“Any activity which is overuse will lead to potential tendon problems and that’s what we’re seeing,” Zarett said.

“Fortunately, I haven’t has any pain or discomfort while using my phone,” one person said.

Zarett suggests heavy phone users try stretching their forearms and wrists after long cellphone sessions.

“It would involve prolonged stretching in this manner right here,” Zarett said. “The elbow has to be straight.”

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He also says bulkier cases can provide better grip and possibly less stress on your hand.

“I compare this to the use of a tennis racket,” Zarett said. “Usually the bigger grip provides you with better control.”

“I have a thick case because I drop my phone so much, so now that I know that, I’m glad I have one,” one woman said.

“But then how is it going to fit into your pocket and then it falls out and then it drops in the toilet?” said another. “There is the greater of two evils, I guess.”

Besides thumb injuries, Zarett says posture problems are even more common, especially with craning the neck forward.