Thin lips refer to lips that appear small, narrow, or lacking in volume, either naturally or due to aging. Genetics is a primary factor, as some people are born with naturally thinner lips. However, as we age, collagen and elastin production decrease, causing lips to lose their fullness and definition. Other contributing factors include sun exposure, smoking, dehydration, and hormonal changes, all of which can accelerate volume loss. For many, thin lips can impact self-confidence and facial balance, but modern aesthetic treatments offer effective solutions to enhance their shape and fullness.