Milium cysts are benign cysts of dead cells trapped under the skin. They primarily affect babies, but can also occur in adults. These microcysts usually disappear spontaneously, but they can still be aesthetically bothersome. How and why do they appear? This article provides some answers.
What are the causes of the appearance of milia?
Published on March 22, 2024, by Kahina, Scientific Editor — 5 min of reading
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The causes behind primary milia.
There have been few studies focusing on the origin of milia. However, certain factors can be suspected. It is believed that primary milia originate from the sebaceous glands of hair follicles. These grains appear spontaneously. They can be congenital and usually resolve within a few weeks or months.
Blockage of hair follicles.
Primary milia can simply appear at any age spontaneously, due to the obstruction of hair follicles. When old skin cells do not shed, they clog the hair follicles. New skin develops over them and traps them under the skin. The dead cells harden and turn into cysts. This can, among other things, be due to the use of creams that are too rich in fatty substances, which will clog the pores attached to the hair follicles. Unlike acne microcysts, they do not contain either sebum or bacteria.
Genetic Origin.
Indeed, the presence of primary milia can also be hereditary, although this situation is rare. The transmission is generally autosomal dominant. Cases of father or mother and son affected have been described. Generally, the appearance of milia by inheritance presents as eruptions from birth and disappear within a few months. Furthermore, studies have shown cases of profuse milia (numerous) linked to genetic skin diseases: the genodermatoses. Among them, we can find type 1 oro-facial digital syndrome and Basex-Dupre-Christol syndrome. Once again, these situations are very uncommon.
The origin of secondary milia.
It is believed that secondary milia originate from the eccrine glands. They are secondary to various processes and appear over time. This is a localised form that can be associated with a disease, medication or trauma.
Trauma.
Traumas can lead to the development of secondary milia. A study conducted by Samuel MONASH has shown that theuse of an abrasive treatment for acne scars could result in the formation of milia. In 25% of patients treated more than once, milia formed two months after the second or third treatment.
Two possible reasons have been identified: some follicles may close due to the abrasive action of the treatment, or pieces of epithelium may have become embedded in the skin during the treatment, which would block the hair follicles. Similarly, the use of cosmetic products that are harsh or abrasive actions on the skin can cause milia.
Exposure to UV rays.
Exposure to UV rays could also contribute to the formation of secondary milia. Similar to trauma, UV rays have numerous abrasive effects, including the induction of cellular lesions and the death of keratinocytes. These situations weaken the skin barrier and hinder cellular renewal, which would promote the appearance of milia.
Long-term application of topical corticosteroids.
It is well-known that the long-term application of topical corticosteroids can lead to skin atrophy. Indeed, corticosteroids cause a loosening and marked degeneration of collagen and elastic fibres around hair follicles, which may be the root cause of milia formation. However, few studies have been conducted and little evidence has been observed.
Dermatological diseases.
Dermatological diseases, such as theepidermolysis bullosa, can be the root cause of the appearance of milia, as previously mentioned. Epidermolysis bullosa is an autoimmune disease. The body, following a disruption of the immune system, produces antibodies against itself, and particularly against the type VII collagen that maintains dermal cohesion. This results in significantskin fragility. This leads to skin fracturing and, consequently, skin detachment at the slightest trauma. The skin's healing will be poor and it is possible to see milia forming. The precise causes, however, remain unknown.
Sources
MONASH S. Formation of milia following abrasive treatment for post-acne scarring. Archives of Dermatology (1953).
TSUJI T. Milia induced by corticosteroids. Archives of Dermatology (1986).
ROSS J. B. & al. Multiple eruptive milia: Report of a case, review of the literature, and a classification. Journal of the American Academy of Dermatology (1997).
BERK D. R. & al. Milia: A review and classification. Journal of the American Academy of Dermatology (2008).
BARBAROT S. & al. Les grains de milium de l’enfant. Annales de dermatologie et de vénéréologie (2009).
GALLARDO AVILA P. & al. Milia. StatPearls (2023).
