What Causes Truncal Acne in Adults
Truncal acne, which refers to acne that develops on the body rather than the face, affects many adults and develops through the same fundamental mechanisms as facial acne. Understanding what causes this condition can help guide effective treatment approaches.
The primary biological process behind truncal acne involves four interconnected factors. First, follicular hyperkeratinization occurs when skin cells don’t shed properly, creating blockages in hair follicles. Second, the skin produces excess sebum, an oily substance that creates an environment where acne-causing bacteria thrive. Third, a bacterium called Cutibacterium acnes colonizes these blocked follicles. Fourth, the body’s immune response to this bacterial presence triggers inflammation, leading to the visible acne lesions.
Sebum production plays a particularly important role in truncal acne development. Androgens, which are hormones present in both men and women, drive sebum overproduction. Additionally, metabolic signals like IGF-1 influence how much sebum the skin produces. The amount of sebum output actually correlates with how severe the acne becomes. This lipid-rich environment in blocked follicles becomes anaerobic, meaning it lacks oxygen, which is exactly the condition where Cutibacterium acnes flourishes.
When the immune system detects the bacteria in these follicles, it activates macrophages, lymphocytes, and neutrophils. These immune cells generate reactive oxygen species and release chemotactic factors that attract more immune cells to the area. This inflammatory cascade can damage the follicle wall, causing it to rupture. When rupture occurs, keratin, lipids, and bacteria spill into the deeper skin layers, creating the papules, pustules, nodules, and cysts that characterize moderate to severe acne.
Several factors can trigger or worsen truncal acne in adults. Friction and sweat from sports gear or tight clothing can provoke acne eruptions. Emotional stress and hormonal fluctuations can exacerbate the condition. Certain medications, particularly some antiepileptic drugs and anabolic-androgenic steroids, can induce or worsen acne. Occlusive products that block the skin can also contribute to development.
It’s important to note that Cutibacterium acnes is present on the skin of most healthy adults. The fact that only some people develop acne indicates that strain-level differences, individual host factors, and the specific microenvironment of the skin determine whether acne actually develops. Different strains of the bacteria show different functional characteristics, and the transcriptional profiles of the bacteria differ between healthy skin and acne-prone skin.
Truncal acne follows the same severity-based treatment approach as facial acne, though the larger surface area and difficulty in applying topical treatments to hard-to-reach areas like the back may require different product formulations. The underlying biological mechanisms remain consistent regardless of body location.
Sources
https://pmc.ncbi.nlm.nih.gov/articles/PMC12735603/
https://pmc.ncbi.nlm.nih.gov/articles/PMC12691598/
https://blogs.the-hospitalist.org/topics/acne
https://www.droracle.ai/articles/593235/what-is-the-recommended-treatment-protocol-for-acne
