How does a sebaceous cyst form?

Particularly found in individuals suffering from cystic or nodular acne, sebaceous cysts present themselves as a hard and rounded lump under the skin, which can measure up to 5 cm. This mass is generally not painful. However, it can happen that a sebaceous cyst becomes inflamed and sensitive to touch. The skin around the cyst then becomes red and warm. It is also possible for a sebaceous cyst to become infected and transform into a boil or skin abscess. Most often, these spots appear on the face, chest or back, areas rich in sebaceous glands.

The formation of a sebaceous cyst results from the rupture of the pilosebaceous follicles due to an accumulation of sebum and keratin.

As a reminder, pilosebaceous follicles are biological structures where hair originates through a process of keratinisation. These skin appendages also include a sebaceous gland, responsible for secreting sebum. This is a fatty substance that contributes to the composition of the hydrolipidic film and serves to protect the skin from dehydration and external aggressions. However, due to hormonal variations or a natural propensity of the skin to produce a significant amount of sebum, it can happen that the latter is no longer able to evacuate and accumulates inside the hair follicle, leading to a gradual swelling of the structure.

In parallel, keratin cells from the superficial layers of the epidermis can also become trapped in the blocked canal. Keratin, a fibrous protein secreted by keratinocytes, plays a significant structural and protective role for the skin. It is notably responsible for the hardness and thickness of the stratum corneum, the most superficial layer of the epidermis. The mixture of sebum and keratin creates a thick and semi-solid mass surrounded by a thin membrane called a capsule or cystic wall. This process can be facilitated by friction and pressure exerted on the skin, which stimulate the migration of keratinocytes into the blocked canal. Indeed, in response to mechanical aggression, keratinocytes proliferate more extensively to reinforce the skin barrier. Moreover, friction creates micro-lesions in the epidermis. This causes a slight swelling of the tissues around the sebaceous canal, reducing the canal's diameter and exacerbating its obstruction.

The gradual accumulation of sebum and keratin is the cause of the swelling of the follicle, leading to the appearance of a small bump under the skin: the sebaceous cyst. As mentioned above, this is surrounded by a thin membrane. The cystic capsule is a shell made of epidermal and keratinised cells that surround the internal mass of sebum and keratin, separating it from the surrounding tissues. It acts as a barrier for the cells and sebum trapped inside the cyst and prevents their dispersion into the surrounding skin tissues. The cyst can remain stable and not evolve for several months. However, any rupture of the capsule, through pressure or friction, can lead to a leak of its contents, thereby triggering a significant inflammatory reaction in the surrounding tissues. It is then appropriate to remove the sebaceous cyst.

How to make a sebaceous cyst disappear?

Some sebaceous cysts disappear on their own, while others continue to grow until they are treated. Without appropriate treatment, a sebaceous cyst can become permanent. It's important to note that one should never attempt to puncture or drain the cyst oneself, as this risks causing an infection and scarring: it is necessary to consult a dermatological surgeon. If the cyst is neither infected nor in an inflammatory stage, it can be directly removed through a surgical procedure that typically lasts between 15 and 20 minutes. In the case of an infected cyst, antibiotics are prescribed. Once the infection is under control, the operation can be performed. However, if the sebaceous cyst drains itself, there is no cause for concern: it is simply recommended to clean the area using a sterile compress and an antiseptic.