SUPPLEMENT INDIVIDUAL ARTICLES: Update on Truncal Acne: A Review of Treatments for a Neglected Disease and the Re-Emergence of Tazarotene

been consensus gaps in recommendations for the assessment and grading of truncal acne with no "gold standard" severity grading tool that is independent of facial acne severity.⁴ To date, only 1 topical retinoid with truncal clinical results has been approved by the US Food and Drug Administration specifically for truncal acne.⁵ There is a need for further studies focused on truncal acne and its treatment. This article serves to highlight salient points of truncal acne with regard to its epidemiology, impact on QoL, pathophysiology, and treatments.

Truncal acne remains underdiagnosed/undertreated and has historically been neglected in scientific investigation.⁶ Current statistics likely underestimate the true prevalence of the disease, and the number of epidemiological studies are limited.³ In a study of 696 adolescent patients ages 14 to 20 years, ~50% with facial acne also presented with truncal acne, while only 3% of patients had truncal-only acne.⁷ A cohort study of 965 patients revealed a prevalence of acne on the back and chest to be 61% and 45%, respectively.⁸ A population-based study of 2,200 adolescents in Brazil, aged 18 years, revealed a high prevalence of truncal acne (back or chest) with ~81% of all adolescents affected (chest or back).⁹ In a prospective observational international study of 2,926 adult female patients with facial acne, aged over 25 years, ~48% also suffered from truncal acne.¹⁰ A cross-sectional study in Turkey of 295 pregnant females aged over 18 years found the severity of truncal acne to be greatest during the third trimester than at any other stage.¹¹

In addition, there appears to be a gender predilection with males being more affected by truncal acne than females.⁷ This is likely overestimated as there are challenges to identifying truncal acne due to the reluctance of some patients to reveal parts of their bodies for numerous reasons (ie, cultural barriers or shame).¹² Notably, barring the Turkish study by Kutlu et al, there is also no mention of the severity of truncal acne in any epidemiological study. As it stands, there is a great need to better characterize the epidemiology of truncal acne globally and to also integrate disease severity into these assessments.

Truncal acne distinctly impacts QoL.¹³ While QoL studies have traditionally focused on facial acne, there has been a recent push for studies focusing on the burden of truncal acne alone or in combination with facial acne. Poorer self-esteem has been associated with more severe acne on the back or chest.¹⁴ This was confirmed in a subsequent study where both males and females who rated their back acne more severely had greater sexual and bodily self-consciousness of appearance.¹⁵ Interestingly, while there was an association between men's self-esteem and truncal acne, self esteem was not significantly associated with facial acne severity. An international cross-sectional survey of 1,309 patients using the acne-specific Comprehensive Quality-of-Life Measure for Facial and Torso Acne (CompAQ), which is the only acne QoL measure that specifies the trunk, revealed that patients with both facial and truncal acne were twice as likely to report a significantly greater impact on QoL than those with facial acne alone.¹⁶ Truncal acne severity also directly correlated with increased psychosocial morbidity irrespective of facial acne severity. Interviews with a subset of patients who had combined facial and truncal acne (N=694) revealed that about 50% reported feelings of embarrassment, self-consciousness, and low confidence.¹⁷ Furthermore, approximately 10% of patients with truncal acne exhibit scarring, further impacting QoL.⁷ It is clear that there is both a physical and psychological burden of truncal acne that leads to feelings of stigmatization, avoidance of social interaction, and depression.¹⁸

Truncal acne is thought to be due to the same 4 major pathogenic mechanisms as facial acne, according to expert consensus opinion.⁴ These include: (1) increased sebum production, (2) abnormal keratinization, (3) Cutibacterium acnes colonization of pilosebaceous unit, and (4) inflammation. Treatments are aimed at mitigating 1 or more of these mechanisms, and treatments that holistically address the greatest of components, such as retinoids, tend to be more efficacious and have longer-lasting remission. However, there does exist a physiologic difference in sebum production between the face and trunk that could theoretically give rise to differences in treatment response. Interestingly, sebum secretion is lower in truncal acne sites than facial acne sites, but no significant correlation was found between sebum secretion and truncal acne lesions.¹⁹ This implies that mechanisms other than sebum production (ie, abnormal keratinization, inflammation, and C. acnes colonization) may have a predominant role in truncal acne pathogenesis. Truncal skin also has a lower pH than facial skin; yet there was no significant correlation between truncal sebum production and pH.²⁰ With regard to pH, it has been established that increased skin pH is associated with facial acne.^21-22 Increased pH is