How can a blackhead develop?

Blackheads (open comedones) are retentional lesions of the epidermis. They most commonly appear on combination to oily skin, characterised by a high production of sebum and more visible pores, but all skin types can be affected. They are found mainly in the T‑zone, which corresponds to the forehead, nose and chin, where the concentration of sebaceous glands is particularly high. This density promotes increased sebum secretion, which can contribute to the obstruction of pores.

This phenomenon is often accompanied by a disruption of the skin’s natural desquamation, the process by which it eliminates its dead cells. Their accumulation, combined with excess sebum, forms a plug within the pilosebaceous follicle. Exposed to the air, this mixture gradually oxidises and turns black. Several factors can promote this hyperséborrhea and the formation of comedones, in particular hormonal fluctuations, certain dietary factors, pollution and exposure to UV radiation.

Did you know? A blackhead measures between 1 and 3 mm in diameter, and its colour is due to the oxidation of sebum upon contact with the air.

Depending on the circumstances, the blackhead can develop in several different ways.

First possible development: The blackhead resolves.

The first possible development of the blackhead, and the most favourable, is its elimination from the pore, whether it is spontaneous or mechanically assisted. Over time, the plug composed of sebum that has become oxidised, together with dead cells, can gradually migrate towards the surface of the skin under the effect of epidermal renewal. This slow process depends in particular on the rate of desquamation and on the balance of sebum production. In some cases, the comedo can therefore be expelled naturally, but this outcome may take several weeks, or even several months.

Mechanical extraction, particularly using a comedone extractor, helps speed up this process by applying controlled pressure around the pore, which results in the rupture of the plug and the expulsion of the follicular contents in the form of a filament. However, this procedure is not without consequence: excessive or poorly directed pressure can damage the wall of the pilosebaceous follicle, promote an inflammatory reaction, or lead to the formation of micro-lesions.

For this reason, it is recommended not to manipulate blackheads yourself, but to entrust their removal to a dermatologist.

Second possible development: The blackhead becomes inflamed.

The blackhead may progress into an inflammatory lesion, marked by the appearance of a red spot that is sensitive to touch. This transformation is mainly driven by the proliferation of the bacterium Cutibacterium acnes, which is naturally present within the skin microbiota. In a sebum-rich environment, such as that of the obstructed follicle, this bacterium encounters favourable conditions for its growth. It hydrolyses the triglycerides in sebum into free fatty acids, irritating compounds capable of damaging the follicular wall and triggering a local inflammatory response.

This inflammation is accompanied by an infiltration of immune cells and the release of pro-inflammatory mediators, which result in redness and swelling. When the inflammation remains superficial, it appears in the form of papules and pustules. By contrast, if it extends deeper, it can lead to the formation of larger and more painful nodules , and even to cystic lesions. The severity of this progression depends in particular on the bacterial load, the quantity of sebum present, and the individual reactivity of the immune system.

Third possible development: The blackhead becomes infected.

Beyond the inflammation linked to Cutibacterium acnes, a blackhead can also progress into a true infection, such as folliculitis, often promoted by repeated manipulation. Touching, squeezing, or attempting to extract a comedone with the fingers exposes the follicle to exogenous micro-organisms, particularly bacteria present on the hands or under the nails. This contamination can lead to a worsening of the initial inflammatory reaction and encourage the development of more extensive lesions.

Moreover, mechanical manipulation can weaken or even rupture the wall of the pilosebaceous follicle. This rupture releases the contents of the comedone — sebum, keratin and bacteria — into the dermis, where they are then recognised by the body as foreign material. This triggers a more intense inflammatory reaction, sometimes associated with a secondary infection, and increases the risk of residual marks.

This is why it is important not to touch your blackheads, especially not with unwashed hands.

A study to investigate further the development of blackheads.

Although scientific studies on the progression of blackheads are scarce, there is a study conducted in 1974 by DURR and his team in an adolescent, which made it possible to track the evolution of 30 open comedones. Through repeated photographs, the researchers observed that blackheads could persist in a non-inflammatory state for several weeks, or even several months — some remaining stable for at least 98 days — while gradually increasing in diameter. Subsequently, these lesions, even without being manipulated, frequently progressed towards inflammatory forms, characterised by the appearance of erythema and oedema, and then towards pustular lesions.

The results also show that the mean time for an inflammatory lesion to progress to resolution is approximately 13 days.

Furthermore, a trend was observed: the longer a comedone persists in a non-inflammatory state, the more the subsequent inflammatory and pustular phase tends to be prolonged. Although these data are based on observations from a single patient, which limits their generalisability, they suggest that open comedones are dynamic lesions liable to progress spontaneously towards inflammatory forms, and that their early removal, when carried out in a non-traumatic manner, could reduce this risk of progression.

• DURR N. P. & al. The natural evolution of comedones into inflammatory papules and pustules. Journal of Investigative Dermatology (1974).

• DOSHI N. B. & al. New researches on acne vulgaris. Research Journal of Pharmacology and Pharmacodynamics (2011).

• LIU Y. & al. Complementary therapies for acne vulgaris. The Cochrane Database of Systemic Reviews (2015).