Wearing noise-cancelling headphones for long stretches of time is safe, sound-wise. However, we do recommend being careful with what situations you use ANC — if you're walking around in a city, for instance, spatial awareness doesn't hurt. You'll also want to avoid blasting music all day to spare your ear drums from damage. Likely, the bigger issue you'll run into is comfort. We recommend trying out a pair from the Bose QuietComfort line if you're particularly sensitive to the sensation of wearing headphones or earbuds for long stretches of time.