Scientists Still Don't Really Know What Causes Acne

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Acne is the most common skin condition in the United States—it affects some 50 million faces each year, according to the American Academy of Dermatology. But it’s also one of the most complicated, as its causes and effective treatments seem to differ from person to person.

Any middle schooler with an internet connection knows that papules, pustules, and blackheads start to form when dead skin cells and oils clog the tiny hair follicles that dapple our face and upper body. This creates the perfect space for a common microbe, Cutibacterium acnes, to dig in. But only some clogged pores go on to become swollen, red pimples. That happens when our own immune cells rush in, triggering inflammation. Even for dermatologists, the intricacies of this immune response still aren’t clean, clear, or under control.

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Traditionally, doctors have thought of acne as a chronic skin condition, like psoriasis, with its signature scaly rash, or rosacea, which causes redness and bumps on the face. But in a new paper, published Thursday in the journal Trends in Immunology, a team of Hungarian scientists argue that acne is more akin to braces or promposals: a “natural, transient inflammatory state,” ostensibly important to adolescent development. Using existing research on animals models, experiments on human skin samples, and genetic data, the researchers conclude it all comes down to age-related changes in the skin’s microbiome.

Most people go through childhood with unblemished skin, but something changes with puberty. Specifically, the sebaceous glands. These microscopic sacs, which are attached to hair follicles, pump out oil to keep skin lubricated. While they serve up dewy Glossier lewks across our lifespan, the glands are particularly aggressive in puberty, when our systems are flooded with androgen hormones, which stimulate sebum production among other transformative functions.

The authors argue that these adolescent oil slicks give lipophilic (literally fat-loving) microorganisms like C. acnes the fuel they need to dominate their environment. But it’s not just any C. acnes that proliferates: recent genomic evidence indicates the bacteria exists in many different strains, some of which are beneficial and others that are more likely to trigger inflammation. Sensing the microbiome is out of whack, the immune system then rushes in to battle, pimpling your skin in the process.

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“It’s actually a very interesting proposition as to why we get acne,” Suzan Obagi, a professor of dermatology at the University of Pittsburgh Medical Center and director of the UPMC Cosmetic Surgery & Skin Health Center, told Gizmodo. “One of the things we’re realizing more and more is the importance of this balance between humans and the microbiome.”

These greasy teen years don’t last forever, of course. Sebum production naturally tapers off as puberty wanes. The researchers think this explains why 85 percent of teenagers experience acne, but as many as 50 percent of those cases resolve spontaneously. While it may be a physically and psychologically traumatic condition to endure, the paper speculates acne could be a learning experience for the immune system, which leads to the crystal clear skin we expect from adulthood. Except... that’s not how it always works out.

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“I disagree with the transient element,” Adam Friedman, a dermatologist at George Washington University School of Medicine who was not involved in the new paper, told Gizmodo. “As a practicing dermatologist, the number one patient I see is an adult, not a teenager.” While some people may outgrow acne seemingly overnight, many patients need a skincare regimen or prescription treatments to keep pimples at bay in their 20s and 30s, and in some cases, even into their 40s and 50s. “I think a lot of people underestimate acne,” Friedman said. “It can have long-lasting implications,” including scarring and discoloration.

Other dermatologists were skeptical of the paper’s emphasis on sebaceous glands, perhaps to the exclusion of other important pathways. Whitney High, a dermatologist at the University of Colorado who was not affiliated with the research, told Gizmodo that the paper overlooks the crucial role of hormones, which can alternately aggravate or alleviate acne, especially in women. And Friedman noted recent research showing C. acnes can produce short-chain fatty acids that disrupt immune regulation in sebaceous cells was absent from the study. (Andrea Szegedi, the corresponding author on the paper, declined to comment for this story.)

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“This is a very hot topic,” Friedman said. Traditionally, doctors have prescribed acne patients retinoids, salicylic acid, and systemic antibiotics like tetracycline. In recent years, however, dermatologists have realized their field is an outsized contributor to antibiotic resistance, in part because people with acne are often on antibiotics for months or even years. But the growing recognition that acne is caused, at least in part, by a disrupted microbiome (and not, as the popular mythology goes, greasy foods or poor hygiene) means some doctors are changing course.

Instead of destroying bad bacteria, Friedman said, they want to replenish what’s good. He described modern approaches designed to fight acne by helping the skin microbiome maintain balance, such as probiotics, made from living microorganisms that encourage the growth of beneficial bacteria and fungi, and prebiotics, derived from compounds in food that serve a similar purpose. These solutions are “still in their infancy,” Friedman said, but the message is clear: you can teach old skin new tricks.

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Even as acne treatments become more sophisticated, the disease has eluded scientists’ attempts to fully understand it. And much to the chagrin of pimple sufferers everywhere, a foolproof cure doesn’t seem to be anywhere in sight.

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About the author

Eleanor Cummins

Freelance science writer obsessed with overlooked history, Pokémon, and everyday body horror.