Head down, thumbs busy, screen inches from your face for hours a day.
A phone is light, but holding your head bent over it for hours is not. Heavy use loads your neck, works the tendons at the base of your thumb, dries and tires your eyes, and pushes bedtime later. Most of the fixes are small changes in how and when you hold it.
Your head weighs about as much as a bowling ball. When you tilt it forward to look at a phone in your lap, the muscles at the back of your neck work much harder to hold it. Hours of this a day are linked to neck and upper back pain, sometimes called "text neck".
Scrolling and typing with one thumb while gripping the phone in the same hand repeatedly loads the tendons along the thumb side of your wrist. Pain there, especially when you make a fist or turn your wrist, can be De Quervain's tenosynovitis.
Reading small text up close for long periods makes your focusing muscles work hard, and you blink less while you concentrate. Dry, gritty eyes, blurry vision and headaches can follow.
Scrolling in bed keeps your mind engaged and pushes bedtime later, and bright screens in the evening can delay the release of melatonin, your body's sleep signal. The result is often less sleep than you meant to get.
Long listening at high volume through earbuds can damage the hair cells in your inner ear, and that damage is permanent. Ringing or muffled hearing after listening is an early warning.
See a doctor or physical therapist for neck pain that spreads into an arm, numbness or tingling in your hand, thumb or wrist pain that lasts more than a few weeks, or ringing in your ears that does not fade.