Association between Acne and Smoking: Systematic Review and Meta-Analysis of Observational Studies
Acne is a chronic inflammatory disease that primarily affects areas of the skin with abundant sebaceous glands. It is a condition that not only causes physical discomfort but also leads to permanent atrophic or hypertrophic scars, which can have serious psychosocial consequences and significantly reduce the quality of life for patients. While acne typically fades after puberty, it can persist into middle age for some individuals. The development of acne is influenced by a combination of endogenous and exogenous factors, including occupational exposures, birth control pills, diet, certain cosmetics, and the menstrual cycle in women.
The relationship between smoking and acne has been a topic of debate in the medical community. Some studies suggest that smoking exacerbates acne, while others have found no significant association or even a protective effect. To date, three systematic reviews have been conducted on this topic. The first, by Mannocci et al. in 2010, analyzed six cross-sectional studies and found no significant correlation between smoking and acne. A second study in 2015 suggested that smokers, particularly males, had a higher risk of developing acne, but this conclusion was based on only three case-control studies, making it less reliable. A third meta-analysis by Bhutani et al. found inconclusive evidence regarding the impact of smoking on acne risk. Given these conflicting findings, the current study aims to provide a more comprehensive analysis by examining the relationship between smoking and acne across different methodological characteristics of observational studies.
This meta-analysis was conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. A comprehensive search of databases, including the Cochrane Library, PubMed, Ovid, and EMBASE, was performed up to June 2019. The search terms used were: (acne OR acne vulgaris OR common acne) AND (smoking OR cigarette OR tobacco OR nicotine). There were no language restrictions imposed. Studies were included if they were observational studies reporting the relationship between acne and smoking, provided independent estimates of the association, or contained sufficient data to calculate these estimates. Non-original articles, reviews, and duplicated publications were excluded. Special types of acne, such as acne inversa, acne medicamentosa, and acne cosmetica, were also excluded. The exposure of interest was a history of cigarette smoking, and smoking status was classified as smoking (current smokers) and non-smoking (never smoked or quit smoking).
Two authors independently extracted data and assessed the methodological quality of the included studies. Disagreements were resolved through consultation, and if necessary, a third author was involved. The Newcastle-Ottawa Scale (NOS) was used to evaluate the quality of case-control studies, while the Agency for Healthcare Research and Quality (AHRQ) was used for cross-sectional studies. The analysis was performed using Review Manager version 5.33.
A total of 20 studies met the inclusion criteria, and after excluding three articles with similar data, 17 studies were included in the final analysis. The studies were distributed across Europe and Asia and included both small and large sample sizes, ranging from 98 to 10,521 participants. The subjects were not limited by gender or age, and both adolescent (aged 12–25 years) and adult (aged >25 years) acne patients were included. The quality assessment of the included studies revealed that the cross-sectional studies had AHRQ scores ranging from 5 to 6, indicating moderate quality. Among the case-control studies, five had NOS scores of 5 or higher, indicating high quality, while one study had a score of 4, indicating low quality. One case-control study did not have the full text available and was not graded.
The pooled odds ratio (OR) for smoking in patients with acne compared to those without acne was 1.21 (95% confidence interval [CI] 0.93–1.57). When analyzed separately, the pooled ORs for case-control studies and cross-sectional studies were both 1.21 (95% CI 0.81–1.81 and 0.84–1.74, respectively). Significant heterogeneity was observed in the overall results and subgroup analyses. In the subgroup analysis by age, the pooled OR for smoking in adults with acne was 1.43 (95% CI 1.10–1.87), while for adolescents, it was 1.04 (95% CI 0.79–1.38). Heterogeneity was significant in both subgroups. Geographic subgroup analysis revealed that the pooled OR for smoking in acne patients was 2.60 (95% CI 1.90–3.56) in Asia and 1.04 (95% CI 0.79–1.38) in Europe. Heterogeneity was not observed in the Asian population but was significant in the European population. The funnel plot was symmetrical, indicating no clear evidence of publication bias. Sensitivity analysis showed that one study had an undue influence on the summary ORs in the Asian population. After excluding this study, smoking became a significant risk factor for acne in this population.
The findings of this meta-analysis suggest that smoking does not have a protective effect on acne risk. Instead, smoking was identified as a risk factor for acne in adults and in the Asian population. However, no significant association was observed in the European population, which may be due to regional differences, genetic factors, or variations in smoking habits. The specific mechanisms linking smoking and acne remain unclear. Nicotine and other components in cigarette smoke can cause vasoconstriction and hypoxemia, and they have anti-inflammatory effects on neutrophil and lymphocyte chemotaxis. However, keratinocytes have nicotine acetylcholine receptors, which can induce hyperkeratosis at high concentrations. Additionally, cigarette smoke contains arachidonic acid and polycyclic aromatic hydrocarbons, which can stimulate the phospholipase A2-dependent inflammatory pathway and exacerbate acne.
This study has several limitations. The results are based on observational studies, which may be subject to bias due to physician diagnoses and patient self-reports of acne. Some studies had small sample sizes, which may have introduced selection bias. Larger population studies are needed to confirm these findings. Additionally, it is unethical to conduct prospective clinical studies on the relationship between smoking and acne due to the known adverse health effects of smoking. Nonetheless, this study provides valuable information that can be used in anti-smoking campaigns and to educate the public about the potential risks of smoking on skin health.
In conclusion, this meta-analysis provides evidence that smoking is a risk factor for acne in the Asian population and in adults. However, further research is needed to confirm these findings and to elucidate the underlying mechanisms. The study highlights the importance of considering smoking as a potential risk factor in the management and prevention of acne, particularly in specific populations.
doi.org/10.1097/CM9.0000000000001286
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