INTRODUCTION
Keratosis pilaris (KP) is a very common, benign dermatological disorder with characteristic small keratotic papules in a folliculocentric pattern.1 This paper aims to explore the relationship between KP and Cutibacterium acnes (C Acnes). It will also explore the role of C Acnes's biofilm in the formation of the biological glue that sticks keratin together in KP.
Overview of Keratosis Pilaris
KP includes a group of follicular disorders, with KP simplex being the most common.2 KP affects approximately 40% of the population and typically begins during childhood and is most severe during adolescence. KP more commonly affects females. In fact, approximately 80% of adolescent females are affected.2
KP is a benign dermatologic condition in which there are multiple hyperkeratotic, folliculocentric papules. The papules are primarily on the extensor surface of the arms, thighs, and buttocks. The first noticeable symptom of KP is the development of rough, folliculocentric keratotic papules that are light pink or flesh colored and contain a finely oiled brittle hair. They typically measure 1-2 mm in diameter. The papules are said to resemble goosebumps. Patients also describe the papules as resembling the texture of sandpaper.2
Erythema is sometimes also associated with KP, but when present, it is typically mild and localized to the perifollicular skin. KP can also occasionally be associated with pruritus, which usually worsens in the winter and improves in the summer. Additionally, KP can be associated with ichthyosis vulgaris, palmar hyperlinearity, and atopic dermatitis.2
Histologically, KP demonstrates a keratin plug that fills the infundibulum of the hair follicle and extends above the skin surface. These plugs can lead to atrophy of the follicular wall, sebaceous gland, and arrector pilorum atrophy.2
The basis of KP is excess keratin production. This excess keratin builds up and surrounds hair follicles, trapping the hair beneath the keratin debris. This leads to the formation of follicular papules. While the cause of this is not entirely understood, inherited mutations in the FLG gene and ABCA12 gene have been linked to the pathogenesis of KP.2 Filaggrin is an epidermal structural protein that allows for aggregation of keratin filaments into keratocytes. This protein can be hydrolyzed into osmotically active amino acids. These amino acids can then provide the skin with moisture, photoprotection, and acidification. Therefore, variations in the filaggrin protein, caused by mutations in the FLG gene, lead to abnormal keratinization, reduced moisture, and alkalinization of the skin. This mutation can also lead to xerosis cutis, dysfunction in the epithelial barrier, bacterial growth, and inflammation.2
Another genetic mutation implicated in KP is the ABCA12 mutation.2 The ABCA12 gene expresses an ATP-binding cassette (ABC) that allows for lipid transfer between the lamellar granules and the granular layer keratinocytes. A mutation in this gene can disrupt the lipid transport and desquamation, which can lead to the dry and solid lesions associated with KP.2
Additionally, sebaceous gland abnormalities, hyperandrogenism, obesity, decreased insulin or IGF-1 have also been implicated in KP pathogenesis.2
Overview of Keratin Structure and Function
Keratin is a fibrous protein and makes up 90-95% of cells in the epidermis.3 Keratins are the intermediate filament proteins of the epithelium and show a great degree of molecular diversity. In the human genome, there are 54 functional keratin genes. Keratin plays a role in the mechanical stability and integrity of epithelial cells and tissues. Keratin can also play a role in regulatory pathways, intracellular signaling, wound healing, and apoptosis.4 The main purpose of keratin, however, is to maintain the architecture of the cell by providing support for the cytoskeleton of cells and tissues, especially when they incur mechanical stress.3
Keratin can be distinguished from other fibrous proteins by its high cysteine residue content. These cysteine residues form disulfide bonds and contribute to mechanical, thermal, chemical, and water stability.3
Overview of Keratosis Pilaris
KP includes a group of follicular disorders, with KP simplex being the most common.2 KP affects approximately 40% of the population and typically begins during childhood and is most severe during adolescence. KP more commonly affects females. In fact, approximately 80% of adolescent females are affected.2
KP is a benign dermatologic condition in which there are multiple hyperkeratotic, folliculocentric papules. The papules are primarily on the extensor surface of the arms, thighs, and buttocks. The first noticeable symptom of KP is the development of rough, folliculocentric keratotic papules that are light pink or flesh colored and contain a finely oiled brittle hair. They typically measure 1-2 mm in diameter. The papules are said to resemble goosebumps. Patients also describe the papules as resembling the texture of sandpaper.2
Erythema is sometimes also associated with KP, but when present, it is typically mild and localized to the perifollicular skin. KP can also occasionally be associated with pruritus, which usually worsens in the winter and improves in the summer. Additionally, KP can be associated with ichthyosis vulgaris, palmar hyperlinearity, and atopic dermatitis.2
Histologically, KP demonstrates a keratin plug that fills the infundibulum of the hair follicle and extends above the skin surface. These plugs can lead to atrophy of the follicular wall, sebaceous gland, and arrector pilorum atrophy.2
The basis of KP is excess keratin production. This excess keratin builds up and surrounds hair follicles, trapping the hair beneath the keratin debris. This leads to the formation of follicular papules. While the cause of this is not entirely understood, inherited mutations in the FLG gene and ABCA12 gene have been linked to the pathogenesis of KP.2 Filaggrin is an epidermal structural protein that allows for aggregation of keratin filaments into keratocytes. This protein can be hydrolyzed into osmotically active amino acids. These amino acids can then provide the skin with moisture, photoprotection, and acidification. Therefore, variations in the filaggrin protein, caused by mutations in the FLG gene, lead to abnormal keratinization, reduced moisture, and alkalinization of the skin. This mutation can also lead to xerosis cutis, dysfunction in the epithelial barrier, bacterial growth, and inflammation.2
Another genetic mutation implicated in KP is the ABCA12 mutation.2 The ABCA12 gene expresses an ATP-binding cassette (ABC) that allows for lipid transfer between the lamellar granules and the granular layer keratinocytes. A mutation in this gene can disrupt the lipid transport and desquamation, which can lead to the dry and solid lesions associated with KP.2
Additionally, sebaceous gland abnormalities, hyperandrogenism, obesity, decreased insulin or IGF-1 have also been implicated in KP pathogenesis.2
Overview of Keratin Structure and Function
Keratin is a fibrous protein and makes up 90-95% of cells in the epidermis.3 Keratins are the intermediate filament proteins of the epithelium and show a great degree of molecular diversity. In the human genome, there are 54 functional keratin genes. Keratin plays a role in the mechanical stability and integrity of epithelial cells and tissues. Keratin can also play a role in regulatory pathways, intracellular signaling, wound healing, and apoptosis.4 The main purpose of keratin, however, is to maintain the architecture of the cell by providing support for the cytoskeleton of cells and tissues, especially when they incur mechanical stress.3
Keratin can be distinguished from other fibrous proteins by its high cysteine residue content. These cysteine residues form disulfide bonds and contribute to mechanical, thermal, chemical, and water stability.3
