The forehead – the area below the hairline and above the eyes – is an important part of the head. Anatomically, it is formed by the frontal bone, which provides bony protection for the brain and frontal lobe. The frontal bone also forms the upper part of the eye sockets, including the area of the eyebrows. It contains the frontal sinus, an air-filled cavity that belongs to the paranasal sinuses.

The frontal bone can be divided into three parts:

• Squama frontalis: the frontal part of the hairless forehead
• Pars orbitalis: the upper part of the eye sockets
• Pars nasalis: the upper part of the nasal region including the connection to the airways

The skin of the forehead contains sebaceous glands, sweat glands and a network of blood vessels. Beneath it lies a superficial muscle, the frontalis muscle (Musculus frontalis).

The frontalis muscle is a so-called cutaneous or skin muscle. It consists of striated muscle fibres located between the skin and the fascia. Unlike many other muscles, skin muscles are not directly attached to the skeleton and primarily serve to move the skin.

In humans, the cutaneous musculature is only relatively weakly developed because we can reach almost every part of the body with our hands. Many mammals have more pronounced skin muscles extending across the head, neck, shoulders and abdomen, for example to twitch the skin and repel insects. In humans, this type of musculature is particularly important for facial expression.

The frontalis muscle (Musculus frontalis) lies beneath the scalp and fascia in the forehead area. Because it is a cutaneous muscle, it is not attached directly to the skeleton. As part of the facial-expression muscles, it plays an important role in facial expression and in communicating emotions. For example, the frontalis muscle allows us to wrinkle the forehead and raise the eyebrows, which is why it is also referred to as an eyebrow elevator.

We express emotions through facial movements. These movements are produced by contraction of facial muscles such as the frontalis muscle. When a facial muscle contracts, the skin folds in certain areas. Initially, the resulting line disappears again when the muscle relaxes. Collagen fibres in the connective tissue are particularly important for this elasticity.

As part of the natural ageing process, however, the skin gradually loses firmness and elasticity because the body produces less collagen and the collagen fibres receive less oxygen and nutrients. Expression lines that were initially temporary therefore become less able to smooth out completely and can eventually remain visible even at rest.

Forehead wrinkles develop over the years through repeated facial movements. Examples include frowning or repeatedly raising the eyebrows while concentrating, thinking or speaking. Each movement of the frontalis muscle causes the skin to fold, and these folds can gradually become etched into the skin.

Patients with hooded eyelids may also tend to develop more pronounced forehead lines because they raise their eyebrows more often in an attempt to lift the upper eyelid. This can temporarily improve the field of vision and relieve the eyes, but it also increases activity of the forehead muscle.

It is not possible to prevent forehead wrinkles completely as we age. However, a healthy lifestyle, sufficient sleep, regular exercise, a balanced diet and appropriate skincare can help delay their development. Consistent sun protection is also important, as is adequate fluid intake.