What is Acne?

whitehead pimpleAcne (Acne vulgaris) is a difficult to treat and often debilitating disease that affects the skin, usually the face.

In most cases, acne is an infection of the sebaceous gland and/or the hair follicle.  This infection is often accompanied by varying degrees of inflammation, which present as more severe acne symptoms.  This inflammation is part of the immune response to the bacteria and is usually characterized by swelling, redness, pain and an infiltration of white blood cells (pus).  Often times the bodies’ own immune response causes more damage and discomfort than the infection itself.

There are several different manifestations of acne with varying degrees of severity.  Acne can range from small patches of red skin with tiny bumps to large, painful and scarring cysts.   Different types of acne can have profoundly different underlying causes and understanding precisely what type of acne you have can help you identify what solutions are going to have the best chance of being effective.

Type 1 Acne

✓ Minimal inflammation.
✓ Minimal affected area.
✓ Not painful.
✓ Irregular outbreaks.

Type 1 acne is the most mild form of acne and generally is the least damaging and easiest to treat form of the disease.  It is characterized by a lack of inflammation and is usually not particularly painful.  The area of the body affected by the acne is usually limited.  This type of acne is often transient and often resolves on its own after about a week.

Non-inflamed blackheads and small red bumps (papules) are common with Type 1 acne.  This form of acne appears to be particularly common in females and often affects the forehead, cheeks, nose and neck.  Over the counter treatment topical treatments such as benzoyl peroxide and salicylic acid washes are often effective at resolving the problem.  Topical antibiotics such as clindamycin and erythromycin are also often effective, but may not be necessary.

Type 2 Acne

✓ Mild inflammation.
✓ Some painful pimples.
✓ Regular outbreaks.

A common manifestation of the disease, Type 2 acne is similar to Type 1 acne, but is characterized by increased levels of inflammation and redness.  Pimples can range from small red bumps to medium sized whiteheads.

Unlike Type 1 acne blemishes, the increased inflammation causes pimples that are often  painful to the touch.  Over the counter topical treatments are often partially effective at decreasing the severity and duration of outbreaks, but are frequently inadequate.  Topical antibiotics and topical retinoids (e.g. Retin-A) can be quite effective.  In some instances it may be necessary to explore oral antibiotics or oral retinoids, if the acne is not responsive to treatment.  In general, Type 2 acne is minimally scarring if allowed to resolve on its own.  However, it is important to practice good hygiene and avoid exacerbating the situation by “popping” pimples without cleaning and sterilizing the area before and after.

Type 3 Acne

✓ Large, painful pimples.
✓ Nodular pimples.
✓ Frequent outbreaks.

Type 3 acne is characterized by the presence of mid sized to large nodules and pustules that are frequently painful.  In Type 3 acne, pimples are often associated with significant amounts of inflammation.

Large whiteheads and large, painful red bumps are common in patients with Type 3 acne.  Individual pimples can often take a long time to resolve, sometimes up to 10-14 days.  In type 3 acne, much of the inflammation and infection originates deeper in the tissue than in Types 1 and 2, often localizing in the dermis and sub-cutaneous fatty tissue.  Because of this, type 3 acne is usually unresponsive to over the counter topical medications.  Likewise, the efficacy of topical antibiotics and topical retinoids is often limited.  In many cases, oral antibiotics and oral retinoids are the only effective treamtents for Type 3 acne.

The increased inflammation associated with Type 3 acne poses a significant risk of permanent scarring.  Deep seated nodules and postules can cause damage to the structural matrix that underlies the skin, causing pitting, discoloration and the accumulation of scar tissue.

Type 4 Acne

✓ Large and painful nodules.
✓ Pustules and Cysts.
✓ Persistent Outbreak.

The most severe form of the disease, Type 4 acne almost invariably causes permanent skin damage and scarring.  Like Type 3 acne, Type 4 acne is characterized by a deep seated infection and extensive inflammation.  Large cysts, which are essentially large, irregular nodules are a common feature in Type 4 acne.

Type 4 acne is is usually completely non-responsive to over the counter medications.  Topical antibiotics and retinoids are minimally effective, in most cases.  Type 4 acne often requires aggressive oral antibiotic and/or oral retinoid treatments.  Type 4 acne is a serious medical condition that should be evaluated  immediately by a dermatologist, if at all possible.   Type 4 acne can cause extensive damage to the skin and underlying structure, causing heavy scarring.  Type 4 acne is often extremely painful, both physically and emotionally, and should be treated as aggressively as possible.

Whiteheads vs. Blackheads

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Acne at A Cellular Level

At a very basic level, acne results from a combination of factors that result in blocked pores, an accumulation of sebum, bacterial growth and inflammation. Acne generally occurs within the hair follicle, when excess sebum is produced by the sebaceous glands and creates a plug that blocks the follicle.

The plugged follicle creates a micro-environment that favors the growth of certain types of bacteria, such as Propionibacterium acnes and Staphylococcus aureus. The presence of this bacteria triggers an immune response, which is characterized by inflammation, increased blood flow (redness) and the recruitment of white blood cells to the follicle.

Primary inflammation can often cause additional damage to the follicle and surrounding tissue, allowing proliferation of the bacterial infection and in turn inducing further swelling.  In some individuals, this process becomes a vicious cycle and leads to extensive acne and significant damage to the skin and the subcutaneous  tissue.   In these cases antibiotic and retinoid therapies are often necessary to disrupt this cycle, resolve the infection and allow healing of the tissue.

Sebum and a Healthy Follicle

The Sebaceous Glands

Sebum is Produced by Sebocytes - Cells of the Sebaceous Gland (Toth)
Sebum is Produced by Sebocytes – Cells of the Sebaceous Gland (Toth)

In a healthy follicle, the sebaceous gland produces the appropriate amount of sebum to maintain the health of the hair and surrounding tissue, and that sebum is efficiently extruded along with the hair.

In people that suffer from acne, several things can happen that disrupt this delicate balance. Normally, the sebaceous glands are relatively small and produce a minimal amount of sebum. However, in many cases of acne, the primary culprit is an overproduction of sebum.

In some cases, the sebaceous glands grow larger and produce greater amounts of sebum. Excessive growth and proliferation of the sebaceous glands is known as sebaceous hyperplasia. Sebaceous hyperplasia can be triggered by increases in androgen hormones, as happens during puberty. (For more detailed information about sebaceous glands see the In Depth: The Sebaceous Glands page.)


Used pore strip with keratinized sebum plugs
Used pore strip with keratinized sebum plugs

Sebum itself is created by the breakdown of the cells that form the sebaceous gland.  Sebaceous cells replicate at the base of the gland and move up towards the hair follicle as the new cells proliferate.

As the maturing cells of the sebaceous glands approach the hair follicle, they undergo apoptosis and die.  The cells are lipid rich (oil) and the byproducts left over as the cells dissolve composes the sebum that lubricates and protects the hair.  Proliferation of the sebaceous glands causes an increase in the production of sebum, which is often manifested as oily skin and hair.

Sebum can also serve as a nutrition source for bacteria that are capable of living in the hair follicle, such as P. acnes and S. aureus. Excess amounts of sebum can encourage bacterial growth and lead to inflammation, redness and an infiltration of white blood cells (pus).  If the plug in the hair shaft is located near the surface, this process can often lead to the formulation of a surface pustule (whitehead). However, for many people who suffer with nodular and cystic acne, the pustules are often formed deep in the tissue and away from the surface.  (For more detailed information about sebum, see the In Depth: Sebum page.)


Propionibacterium acnes growing in pores produces a fluorescent orange glow when illuminated by ultraviolet light
Propionibacterium acnes growing in pores produces a fluorescent orange glow when illuminated by ultraviolet light

The formation of a plug in the follicle can lead to the accumulation of sebum, bacteria and white blood cells deep within the follicle. In these cases, the result is often the formation of large painful nodules and cysts.

Since acne pustules are surrounded by tissue, it is not easily possible to drain the pus and bacteria to the surface (lance the pimple).  Many times, continued sebum production, bacterial growth and inflammation within a plugged follicle can cause the follicle to rupture and drain into the surrounding tissue.  This process can lead to further inflammation, dissemination of the bacterial infection and progression of the disease.

The cycle of infection, inflammation and damage is responsible for the formation of acne scars.  Patients with severe inflammatory acne symptoms have a high risk of experiencing permanent acne scarring.  The most effective way to prevent acne scars is to effectively treat acne symptoms.

Acne Treatments

For most of the pimples in type 1 and type 2 acne, the blockage and inflammation is relatively close to the surface.  As a result, topical medications are reasonably effective at treating the disease.  However, it is also important to note that most topical preparations are not capable of penetrating deep enough into the tissue to treat nodular and cystic acne.  In these cases, it is often necessary to utilize oral antibiotics to control the bacterial infection and oral retinoids to slow down the growth of the sebaceous glands.

Explore the Science of Acne