Forehead lines are the horizontal indentations that appear across the forehead when we activate the frontalis muscle as we pull certain facial expressions such as raising our eyebrows.
As we age, skin gradually becomes looser as it loses stores of collagen, elastin and subcutaneous fatty tissue, which keeps our skin firm and taut.
Therefore as we repeat these movements countless times a day, everyday, these lines become deeper and more obvious as skin integrity weakens. This eventually leads to permanent lines remaining present, even when expression is not being made.
Exposure to the sun, genetics and smoking can also accelerate and exaggerate this condition.