Why is My Jawline Undefined? An undefined jawline can significantly impact your facial aesthetics, making you appear older and heavier. But why is your jawline still indistinct even if you're already thin? There are numerous reasons for a blurred jawline, including both genetic and lifestyle factors. Causes of a Blurred Jawline • Bone Structure: A naturally receding chin or underdeveloped jawbone can affect the definition of your jawline. • Fat Accumulation: Excessive fat accumulation around the chin can blur the jawline contour and lead to a double chin. • Skin Laxity: Collagen loss and sagging skin can impact the mid-face and lower face contours. • Lifestyle Factors: Poor posture, chronic sleep deprivation, and an unbalanced diet can accelerate facial aging.