Most people can recognize acne when it presents on the face or body. Most people also have the vague understanding that acne is associated with oily skin and an excess production of sebum. But beyond that, few people really grasp what is actually happening at the microscopic level of a pimple.
Understanding the physiological and pathological processes behind acne can help you sort out what treatments and advice can help you make positive changes in your acne. A better understanding of the science of acne can also help you identify the claims that have no basis in scientific reality and should be ignored.
What Causes Acne?
Acne is caused by 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.
Clogged follicles create 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.
The initial inflammation of an acne lesion can cause damage to the follicle and surrounding tissue. This inflammation can then increase the growth of bacteria, which creates a positive feedback loop of additional inflammation. In some individuals, this process becomes a vicious cycle and leads to extensive acne and significant damage to the skin and the subcutaneous matrix that supports healthy skin. Severe and repeated damage that is caused by inflammatory acne lesions can cause permanent acne scars.
Sebum and a Healthy Follicle
Sebum is a mixture of fatty acids and lipids that is essential for lubricating and protecting healthy skin. Sebum is produced by Sebaceous Glands, which are attached to the base of hair follicles. In a healthy follicle, the sebaceous gland produces the appropriate amount of sebum to maintain the health of the surrounding skin, and the sebum is efficiently extruded along with the hair.
For individuals with acne, several things can happen that disrupt the delicate balance of sebum production. Normal sebaceous glands are relatively small and produce a minimal amount of sebum. However, excessive growth of the sebaceous glands (sebaceous hyperplasia) and overproduction of sebum can be an important contributor to acne symptoms. Sebaceous hyperplasia can be triggered by increases in androgen hormones, which is common for males during puberty.
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 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 can present as oily skin and hair.
Sebum can also serve as a nutrition source for bacteria that reside inside 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 a hair follicle is plugged near the surface, this process can often lead to the formulation of a surface pustule (whitehead). However, for many people who suffer with inflammatory acne, the pustules are often formed deep in the tissue and away from the surface. These deep-seated pustules are responsible for nodular and cystic acne symptoms (Acne Types: 3-4).
The deep-seated pustules that form in nodular and cystic acne lesions are surrounded by tissue and it is difficult to drain the pus and bacteria to the surface (eg. “pop” or lance the pimple). Individuals with acne lesions that are significantly inflamed or painful should generally avoid trying to pop these pimples at home. Effectively and safely draining these lesions can reduce symptoms and accelerate healing, but these procedures should be performed by a trained medical professional. 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, worsening acne symptoms and the formation of acne scars.
The human sebocyte culture model provides new insights into development and management of seborrhoea and acne. Zouboulis, et al. 1998.
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Genetic control of sebum excretion and acne—a twin study. Walton, et al. 1988.
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From new findings in acne pathogenesis to new approaches in treatment. Gollnick. 2015.
A systematic review and meta-analysis on Staphylococcus aureus carriage in psoriasis, acne and rosacea. Totte, et al. 2016.
Evolving perspectives on the etiology and pathogenesis of acne vulgaris. Eichenfield, et al. 2015.