Forehead lines are a common sign of skin aging in adults. They are creases in the skin that form above the eyes and brow and usually appear as vertical lines between the brows, or as long lines that extend horizontally across the forehead. Forehead lines are part of the natural aging process. As the skin ages, it loses elasticity and firmness, causing the skin to lose its springiness. As a result, fine lines begin to appear and the skin becomes thinner and drier. Habitual movement of facial muscles is a major cause for the development of forehead lines. Over time, the grooves formed by repeated facial expressions can become permanent lines in your skin. Factors such as chronic sun exposure and smoking can often cause these lines to start appearing earlier. Fortunately, the appearance of facial lines and wrinkles can be reduced with treatment and proper skin care.