In some individuals, these muscles are naturally overactive, causing the mouth corners to rest in a downturned position even when the face is relaxed. This can unintentionally create a tired, unhappy, or stern resting expression despite feeling perfectly content.

 

As the ageing process progresses and facial support diminishes, the downward pull of the DAO muscles can become even more pronounced, contributing to a heavier lower face and more noticeable marionette lines.