No. There have been few if any clinical studies of the effects of noise cancelling headphones on our ears, and any such studies would be time consuming and expensive. Unfortunately, this is not a question we can give an unequivocal answer to. However, most people wearing these headphones will see no ill effects, and if you do experience discomfort after a while, there is always the option to turn the noise cancelling back off. You may also find it useful to switch off the ambient noise when you are asleep or in quiet environments.