Which side of your face is bigger? Lie on that side.

There is no clear scientific evidence to directly support the claim that "you should sleep on the side where your face is larger."

Facial shape and size are influenced by multiple factors, including bone structure, muscle distribution, fat accumulation, and daily habits. From some perspectives, sleeping posture may somewhat influence facial appearance. For example, consistently sleeping on one side may compress that side of the face, affecting blood circulation and lymphatic drainage, which could lead to temporary swelling or slight deformation of the face on that side. However, this situation is usually temporary and the impact is relatively minor.

When it comes to facial asymmetry in size, if it is caused by more fixed factors such as bone structure or fat accumulation, simply changing sleeping posture is unlikely to produce significant results. In such cases, medical aesthetics or surgical interventions might be necessary to achieve improvement. If the asymmetry is caused by daily habits, attempting to change those habits may gradually improve facial symmetry. For example, consciously using both sides of the mouth to chew evenly can help prevent long-term favoring of one side; when sleeping, trying to alternate sleeping positions can help avoid prolonged pressure on one side.