How Acne Develops in the Skin — The Biological Process Behind

To treat acne effectively, it is essential to understand how acne actually forms beneath the skin, long before a visible pimple appears. Acne does not start as a red bump or whitehead; it begins at a microscopic level inside the hair follicle. This process explains why acne can feel sudden on the surface but is, in reality, the result of gradual biological changes.

The Four-Step Mechanism

Acne develops through a four-step mechanism involving sebum overproduction, abnormal skin cell shedding, bacterial activity, and inflammation. These steps occur together, not in isolation, and the dominance of each step determines the type of acne a person develops.

Step 1: Excess Sebum Production (Why Skin Becomes Oily)

Sebum is an oily substance produced by the sebaceous glands to protect and lubricate the skin. Under normal conditions, sebum is beneficial, it maintains skin hydration and barrier function. However, when sebaceous glands become overactive, excess oil accumulates inside the pores.

The most common trigger for increased sebum production is hormonal stimulation, particularly androgens. This is why acne often worsens during:

• Puberty
• Menstrual cycles
• Pregnancy
• Polycystic ovarian syndrome (PCOS)
• High-stress periods

This excess oil is the foundation of both oily skin and acne-prone skin, but oily skin alone does not mean acne. Problems arise when oil becomes trapped inside the follicle.

Step 2: Abnormal Shedding of Dead Skin Cells

Healthy skin constantly sheds dead cells from the surface. In acne-prone individuals, this shedding process becomes disorganized. Instead of being released normally, dead skin cells accumulate inside the follicle and mix with sebum.

This mixture forms a plug, known medically as a microcomedone — the earliest and invisible stage of acne. At this point, there is no redness or pain, but the conditions for acne are already set.

When this plug remains under the skin, it appears as:

• Closed comedones (whiteheads) — Small skin-colored bumps often mistaken as texture

If the plug opens to the surface and oxidizes, it becomes:

• Open comedones (blackheads) — Blackheads are not caused by dirt; their dark color results from oxidation of sebum, not poor hygiene.

Step 3: Bacterial Proliferation Inside the Pore

Once the pore is clogged with oil and dead skin cells, it creates an oxygen-poor environment. This environment is ideal for the growth of Cutibacterium acnes (formerly Propionibacterium acnes), a bacterium naturally present on the skin.

When these bacteria multiply excessively:

• It releases inflammatory byproducts
• The immune system responds aggressively
• The follicle wall becomes weakened

At this stage, acne shifts from non-inflammatory (comedonal acne) to inflammatory acne, and thus increasing the risk of pain, redness, and scarring.

Step 4: Inflammation and Lesion Formation

As bacterial activity increases, the follicle may rupture, spilling its contents into surrounding skin tissue. This triggers visible inflammation and leads to different acne lesions, including:

• Papules (red, tender bumps)
• Pustules (pus-filled pimples)
• Nodules (deep, firm lesions)
• Cysts (large, painful, inflamed swellings)

Cystic acne and hemorrhagic cysts represent severe inflammation and require medical intervention, often involving isotretinoin or specialist-supervised therapy.

Why Some Acne Is Mild and Other Acne Is Severe

The severity of acne depends on:

• The depth of follicular blockage
• The intensity of inflammation
• Genetic sensitivity of sebaceous glands
• Immune response of the skin

For example:

• Comedonal acne involves mainly clogged pores
• Inflammatory acne includes papules and pustules
• Nodular or cystic acne extends deeper into the dermis
  

This explains why treatments vary and range from salicylic acid face wash and adapalene gel for mild acne, to oral medications for severe cases.

Oily Skin Isn’t Always the Villain in Acne

Oily skin is a contributing factor, not a direct cause, of acne. Excess sebum increases the likelihood of pore blockage, but acne only develops when oil combines with abnormal cell shedding and inflammation.

This is why some people have oily skin without acne, while others with less oil still experience persistent breakouts due to cell turnover issues or inflammatory sensitivity.

Why Acne Keeps Coming Back

Acne often recurs because:

• The underlying mechanisms remain active
• Treatments are stopped too early
• Only visible pimples are treated, not microcomedones
• Hormonal or lifestyle triggers are unaddressed

So, an effective acne management focuses to prevent new lesions, not just to clear the existing ones.