Acne Pathogenesis Overview

What is acne vulgaris?

• A common chronic inflammatory skin condition.

• It affects the pilosebaceous unit.

• It causes comedones and inflammatory lesions.

• It is most common on the face, back, and chest.

What is the pilosebaceous unit?

• The skin structure where acne develops.

• It consists of a hair follicle, the hair shaft, and a sebaceous gland.

• It is found in high density on the face, back, and chest.

What is a hair follicle?

• A tube-like structure in the skin.

• Hair grows from it.

• The sebaceous gland opens into it.

• It is part of the pilosebaceous unit.

What is a sebaceous gland?

• A small gland attached to a hair follicle.

• It produces sebum.

• It is found in high density on the face, back, and chest.

What is sebum?

• An oily substance produced by sebaceous glands.

• It is made mainly of lipids.

• It normally lubricates the skin and hair.

• In acne, it can be produced in excess and have an altered composition.

What is an androgen?

• A type of hormone.

• Testosterone is an example.

• Androgens stimulate sebaceous glands.

• They increase sebum production.

What is a keratinocyte?

• The main cell type in the epidermis.

• It produces keratin.

• It lines the hair follicle.

• Abnormal shedding of keratinocytes is important in acne.

What is keratinization?

• The normal process in which keratinocytes mature and move outward.

• It helps form the outer layers of the skin.

• In the hair follicle, keratinocytes are normally shed in a controlled way.

What is a comedo?

• A blocked hair follicle.

• It contains sebum and keratin.

• It can be open or closed.

What is a microcomedone?

• The earliest acne lesion.

• It is a microscopic blocked follicle.

• It forms from hyperkeratinization and sebum.

• It is the precursor to visible comedones and inflammatory lesions.

What is Cutibacterium acnes?

• A bacterium that normally lives on the skin.

• It colonises sebaceous follicles.

• In acne, it can overgrow in blocked follicles.

• It is often abbreviated to C. acnes.

What is inflammation?

• A response by the immune system to irritation, injury, or a trigger.

• It causes redness, heat, swelling, and pain.

• In acne, it is triggered by the blocked follicle and C. acnes.

What is immune dysregulation?

• An abnormal or excessive immune response.

• The immune system overreacts to a trigger.

• It contributes to inflammatory acne.

What are the four core pathogenic factors in acne?

• Excess sebum production and altered lipids.

• Follicular hyperkeratinization.

• Microbial colonization by C. acnes.

• Inflammation and immune dysregulation.

How do the four core factors interact in acne?

• Excess sebum and altered lipids create a favourable environment.

• Follicular hyperkeratinization blocks the follicle.

• C. acnes overgrows in the blocked, sebum-rich follicle.

• Inflammation and immune dysregulation produce visible inflammatory lesions.

What is excess sebum production?

• Sebaceous glands produce more sebum than normal.

• It is driven mainly by androgens.

• It often begins at puberty.

• It creates a sebum-rich environment in the follicle.

How do androgens contribute to acne?

• Androgens stimulate sebaceous glands.

• This increases sebum production.

• Androgen levels rise at puberty.

• This helps explain why acne often starts in adolescence.

What is altered lipid composition of sebum?

• The quality of sebum changes, not just the quantity.

• The proportions of different lipids are different from normal.

• For example, linoleic acid may be decreased.

• This altered sebum contributes to follicle blockage and C. acnes growth.

How does excess altered sebum contribute to acne?

• It provides nutrients for C. acnes.

• It contributes to plug formation in the follicle.

• It promotes bacterial overgrowth.

• It helps create the environment needed for inflammation.

What is follicular hyperkeratinization?

• Abnormal and excessive shedding of keratinocytes lining the hair follicle.

• The keratinocytes become sticky and clump together.

• They are not shed normally.

• This blocks the follicle opening.

How does follicular hyperkeratinization cause a microcomedone?

• Sticky keratinocytes mix with sebum.

• They form a plug in the follicle.

• The follicle becomes blocked.

• A microcomedone forms.

What is the difference between an open and closed comedo?

• A closed comedo is a whitehead.

• The follicle opening is closed.

• An open comedo is a blackhead.

• The follicle opening is open.

• The dark colour in an open comedo is due to oxidised material.

Why is the microcomedone important in acne?

• It is the earliest acne lesion.

• It is the precursor to all visible acne lesions.

• It creates a blocked, sebum-rich environment.

• C. acnes can overgrow inside it.

• It can progress to an inflammatory lesion.

What is microbial colonization in acne?

• C. acnes overgrows in the blocked follicle.

• It is a normal skin bacterium, not simply an external infection.

• It becomes more numerous in the sebum-rich follicle.

• Its overgrowth contributes to inflammation.

Why does C. acnes overgrow in acne?

• The follicle is blocked.

• Excess sebum provides nutrients.

• Altered lipids provide a favourable environment.

• The blocked follicle has a low-oxygen environment that suits C. acnes.

How does C. acnes contribute to acne?

• It metabolises sebum.

• It releases free fatty acids and other products.

• It forms clusters in the follicle.

• It triggers the immune system.

• It contributes to inflammation.

Is C. acnes alone enough to cause acne?

• No.

• C. acnes is normally present on the skin.

• Acne requires interaction with the other core factors.

• Inflammation is needed for inflammatory lesions.

What triggers inflammation in acne?

• The blocked follicle.

• C. acnes and its products.

• Altered sebum composition.

• Activation of the immune system.

What is the role of immune dysregulation in acne?

• The immune system responds excessively.

• Immune cells are recruited to the follicle.

• Inflammatory mediators such as cytokines are released.

• This causes redness, swelling, and pain.

What are inflammatory acne lesions?

• Papules.

• Pustules.

• Nodules.

• They are caused by inflammation around the blocked follicle.

How can inflammation lead to scarring in acne?

• Severe inflammation can damage the follicle wall.

• Follicle contents can spill into the surrounding dermis.

• This causes further tissue damage.

• Tissue damage can lead to acne scars.