It is usually stress or deep focus, not a jaw defect.
The NHS lists stress and anxiety as the most common cause of teeth grinding and clenching, with sleep problems, smoking, and heavy caffeine or alcohol intake as contributors. Awake clenching is the same reflex during the day: concentration and tension tighten the jaw muscles without you noticing. Over time it can wear teeth, trigger temple headaches and earache, and feed temporomandibular disorder. The first-line fix is catching yourself: teeth apart, tongue as a spacer, lips closed, jaw relaxed, plus work on the stress driving it.
What to do
Common questions
Why do I clench my jaw during the day?
Daytime clenching is almost always a stress or concentration habit, not a sign that something is wrong with your jaw. The NHS says teeth grinding and clenching is most commonly linked to stress and anxiety, and daytime clenching is the same behavior while awake: it shows up during focused work, driving, deadlines, and tension, usually without you noticing until your jaw aches or a partner or colleague points it out. Other contributors on the NHS list include sleep problems like sleep apnoea, smoking, and lots of caffeine or alcohol. The habit matters because it loads the jaw joint and teeth for hours: worn or sensitive teeth, jaw pain, temple headaches, and even earache can follow. The fix is awareness plus interruption: set reminders to check in, park your tongue between your teeth so you physically cannot bite down, keep lips closed and teeth apart, and address the underlying stress. If clenching is damaging teeth or causing real pain, a dentist can fit a guard, and persistent jaw pain or clicking points to temporomandibular disorder, which the NHS notes usually improves with self-care.