Recent studies proposed above-the-neck gestures for people with upper-body motor impairments interacting with mobile devices without finger touch, resulting in an appropriate user-defined gesture set. However, many gestures involve sustaining eyelids in closed or open states for a period. This is challenging for people with dystonia, who have difficulty sustaining and intermitting muscle contractions. Meanwhile, other facial parts, such as the tongue and nose, can also be used to alleviate the sustained use of eyes in the interaction. Consequently, we conducted a user study inviting 16 individuals with dystonia to design gestures based on facial muscle movements for 26 common smartphone commands. We collected 416 user-defined head gestures involving facial features and shoulders. Finally, we obtained the preferred gestures set for individuals with dystonia. Participants preferred to make the gestures with their heads and use unnoticeable gestures. Our findings provide valuable references for the universal design of natural interaction technology.