Fillers are substances used in cosmetic treatments to add volume to different areas of the face, soften wrinkles, and enhance facial features. They are commonly made of hyaluronic acid, a natural substance found in the skin that helps retain moisture and plumpness. Fillers can be injected into areas such as the lips, cheeks, and under-eye area to create a more youthful and rejuvenated appearance. They are a popular non-surgical option for those looking to enhance their facial features without undergoing invasive procedures.