What are the causes of pore dilation?

The correlation between excessive sebum production and pore dilation is well documented. The higher the sebum secretion, the more the pores tend to appear enlarged. Sebum, produced by the sebaceous glands, serves to moisturise and protect the skin. However, when produced in excess, it accumulates on the surface and within hair follicles, which causes a mechanical enlargement of the skin's pores.

In women, this phenomenon can vary throughout the menstrual cycle. Studies have shown that during ovulation, sebum production and pore size are significantly increased. This hormonal variation is partly explained by the rise in luteinising hormone (LH) and follicle-stimulating hormone (FSH), as well as by the gradual increase in progesterone at this stage of the cycle. The oestrogen, at physiological doses, has little effect on sebaceous gland regulation. It is therefore likely the combination of LH, FSH and progesterone that stimulates their activity.

Another key player is Insulin-like Growth Factor 1 (IGF-1), a hormone involved in cellular growth and metabolism. IGF-1 stimulates lipogenesis in the sebaceous glands via activation of the phosphoinositide 3-kinase/Akt pathway, thereby increasing sebum production. Numerous scientific studies have demonstrated a positive correlation between serum IGF-1 levels, facial sebum excretion and pore size. Sensitivity to IGF-1 and the propensity to produce more sebum vary among individuals. Such genetic factors influence the density and activity of the sebaceous glands, as well as the responsiveness of hormonal receptors. Thus, even with similar levels of IGF-1 or sex hormones, some people will develop higher sebum output and more visible pores than others.

The cutaneous ageing is a major factor in pore dilation as it affects both the structure and elasticity of the skin. Enlarged pores are characterised by an uneven skin surface, an abnormal dermo-epidermal junction and an altered extracellular matrix. As a reminder, the extracellular matrix is the network of proteins and polysaccharides that supports the dermal cells of the skin and provides its elasticity and firmness. Researchers have demonstrated a pronounced undulation of the dermo-epidermal junction around the pores, forming a stalagmite-like structure. This configuration, which resembles small vertical projections, is now recognised as a marker of dilated pores and cutaneous ageing. A study conducted by KITAHARA and her team on 138 volunteers of varying ages confirmed that the degradation of skin structure is closely linked to age and pore size.

Cutaneous ageing also leads to a loss of elasticity in the structures around pores. For example, microfibril-associated glycoprotein-1 (MAGP-1), a protein essential for elastic fibre formation, decreases with age around hair follicles and pores, reducing skin tension and promoting their enlargement. Collagen degradation, another protein essential for maintaining the extracellular matrix, also contributes to tissue sagging around pores.

Finally, a low-grade chronic inflammatory mechanism associated with ageing, termed inflammaging, may be involved in pore dilation. This silent inflammation is hard to detect but builds up over time, causing internal damage to the skin. As time passes, the complement system, part of the immune system, becomes persistently activated and leads to an accumulation of pro-inflammatory cytokines and damaged macromolecules that the skin can no longer clear efficiently. More specifically, hyperactivation of the complement system promotes the differentiation of monocytes into activated macrophages, which then release matrix metalloproteinases and reactive oxygen species that degrade the extracellular matrix. In the case of enlarged pores, this chronic inflammation could contribute to the formation of stalagmite-like structures observed at the dermo-epidermal junction, favouring further pore enlargement.

Another important factor influencing the appearance of pores is the thickness of the hairs themselves. Indeed, the size of a pore largely depends on the volume of the hair follicle. This, in turn, is closely linked to that of the dermal papilla, a structure located at the base of the hair follicle. It plays a key role in hair growth. The dermal papilla is a richly vascularised area that delivers the nutrients and oxygen essential for hair growth. The dermal papilla contains cells and extracellular matrix, the number and volume of which directly influence the size of the adult hair follicle. The cells of the dermal papilla express androgen receptors, and androgen action is a major factor in increasing follicle size. Consequently, thicker or more voluminous hairs can visibly enlarge the pore on the surface of the skin.

Thus, the appearance of pores remains strongly influenced by hormonal and genetic factors. The sensitivity of dermal papillae to androgens varies among individuals, as do the density and structure of hair follicles, which explains why some people naturally have more visible pores than others.

Chronic sun exposure is a major driver of skin ageing and contributes to the appearance of enlarged pores. UV rays, particularly UVA, penetrate deep into the dermis and trigger the degradation of collagen and elastin fibres, which are responsible for the skin’s elasticity and firmness. This loss of structural support around hair follicles leads to tissue laxity, making pores more visible. Moreover, UV radiation promotes the generation of free radicals that damage skin cells and the extracellular matrix. This damage not only compromises skin tone but can also exacerbate the effects of inflammaging, already implicated in the formation of stalagmite-like structures around pores.

Furthermore, sun exposure can enhance sebum secretion. Indeed, in response to the sun’s drying effect, the sebaceous glands tend to react by increasing sebum production. Moreover, combined with reduced skin elasticity, this contributes to pore enlargement, particularly in the most sun-exposed areas of the face, such as the forehead and nose. Finally, photo-induced damage accumulates over the years, which explains why pores tend to become more dilated with age, especially in individuals who are regularly exposed to the sun without adequate protection. Prevention therefore relies on daily sun protection and the regular use of antioxidants.

Finally, the skincare routine can influence the appearance of pores. When it is not tailored to the skin type, it may accentuate their dilation and visibility. For example, the use of occlusive or overly rich products for a combination to oily skin promotes the accumulation of sebum and dead cells inside the hair follicles. This leads to a gradual widening of the pore channel, giving the skin surface an uneven texture.

Conversely, some overly aggressive routines relying on highly detergent cleansers or too-frequent exfoliation can impair the skin barrier. Once compromised, the skin responds by producing more sebum to offset the loss of its protective lipids, which contributes to pore dilation. Another bad habit: neglecting exfoliation. While over-exfoliating can weaken the skin, insufficient exfoliation can lead to an accumulation of corneocytes that obstruct the pores. That is why it is generally recommended to perform one to two exfoliations per week.

Discover here our guidance on reducing pore dilation.

• CHUNG K. & al. Sebum output as a factor contributing to the size of facial pores. British Journal of Dermatology (2006).

• KITAHARA T. & al. Age-related changes in the epidermal architecture around facial pores. Journal of Dermatological Science (2008).

• TAKAHASHI K. & al. Analysis of the skin surface and internal structure around facial pores. Skin Research and Technology (2013).

• SEO S. J. & al. Facial pores: Definition, causes, and treatment options. Dermatologic Surgery (2015).

• CHEN Y. & al. Potential role of inflammaging mediated by the complement system in enlarged facial pores. Journal of Cosmetic Dermatology (2023).