Association of fast foods and dairy products in acne severity and scarring: a cross-sectional study

Abstract

Introduction:

The pilosebaceous unit is impacted by the prevalent chronic inflammatory skin condition known as acne vulgaris. The formation of comedones, papules, and pustules are among the clinical signs of acne. Acne is usually thought to be harmless, yet it can leave disfiguring scars and have psychological effects.

Methods:

In our cross-sectional study with 386 participants, we examined acne severity and scarring in relation to variables such as age, gender, family history of acne, and dietary habits (especially fast food and dairy products). The assessments were conducted by a trained medical team and validated by a dermatologist. Statistical analysis was performed using SPSS version 16, with significance set at P < 0.05. Associations were expressed as odds ratios with 95% confidence intervals.

Results:

Moderate acne was the most common presentation (66.6%), followed by mild (31.6%) and severe (1.8%) cases. Scarring was mostly Grade 2 (65.3%), with fewer participants having Grades 1, 3, or 4. In bivariate analysis, higher acne severity was significantly associated with younger age and male gender (P < 0.001). However, multivariate logistic regression revealed no statistically significant associations between acne severity or scarring and age, gender, family history, fast food consumption, or dairy intake.

Conclusions:

In this cohort, no statistically significant association was observed between the consumption of fast foods or dairy products and acne severity. However, these findings should be interpreted cautiously given the methodological limitations. Further research is needed to clarify the potential role of diet in acne development.

Introduction

Acne vulgaris is a common chronic inflammatory skin disorder characterized by comedones, papules, and pustules, mostly affecting the face but also involving the neck, trunk, and upper limbs[1]. It affects 80–90% of teenagers and 40–60% of adults, making it extremely common. Acne is more common in women, especially young girls. Acne affects over 9.40% of people worldwide, making it the eighth most common ailment^[2-4]. Commonly regarded as innocuous, acne can cause psychological distress and scarring that lasts from adolescence into adulthood by negatively impacting emotional health, personality development, social interactions, quality of life, and sexuality^[5-7].

HIGHLIGHTS

• Moderate acne (66.6%) and Grade 2 scarring (65.3%) were the most prevalent among participants.

• Male gender and age below 19 years were significantly associated with greater acne severity and scarring.

• No significant association was found between acne severity and fast food or dairy intake.

• Findings highlight the predominant role of biological factors over dietary habits in acne pathogenesis.

The pathogenesis of acne is multifactorial, involving hormonal changes, increased sebum production, follicular hyperkeratinization, and inflammation. However, the role of dietary and lifestyle factors – particularly fast food and dairy consumption – remains controversial. Dietary factors, particularly high-glycemic foods and dairy intake, have been hypothesized to contribute to acne pathogenesis through hormonal and inflammatory pathways, including stimulation of IGF-1 and increased sebum production[8]. While several Western studies^[6,9] have found associations, evidence from South Asia remains sparse[10]. Nepal represents a valuable context due to its ongoing dietary transition, allowing for examination of both traditional and Western dietary patterns. Understanding dietary influences in this setting may inform culturally specific acne management strategies.

This study aimed to evaluate the association between dietary habits (specifically fast food and dairy intake) and acne severity and scarring among a Nepalese population. The échelle d’évaluation clinique des cicatrices d’acné (ECCA) grading scale was used to assess acne scarring, and the study also examined the influence of age, gender, and family history on acne presentation^[2,11–13]. This study is reported in line with the STROCSS 2025 Guideline Checklist[14]. AI was used only for language polishing while preparing the manuscript and is reported under the TITAN guideline 2025[15].

Methods

Participants and data collection

A cross-sectional study was conducted in 2023 at two dermatology centers in Kathmandu, Nepal. The study aimed to assess the relationship between dietary habits – particularly fast food and dairy intake – and acne severity and scarring in a Nepalese population.

The structured questionnaire was administered by a trained researcher to collect information on age, gender, dietary habits (with an emphasis on fast food and dairy consumption), alcohol use, family history of acne, and other lifestyle factors.

Ethical approval was obtained from the Ethical Review Board of the National Health Research Council (Reference number: 3330). Written informed consent was obtained from all participants or their guardians, and the study adhered to the principles of the Declaration of Helsinki.

This study included individuals aged 12 years and above with clinically diagnosed acne vulgaris who were willing to provide informed consent and could recall their dietary habits, particularly fast food and dairy consumption. Participants were excluded if they had other skin conditions mimicking acne, endocrine disorders influencing acne (such as polycystic ovary syndrome [PCOS]), were on medications known to worsen acne (e.g., steroids), had undergone recent cosmetic procedures, or were on systemic acne treatments within the past three months.

This study utilized a subset of data from a previously published article by the same authors, which investigated dermatological conditions among a larger population. From that dataset, 386 individuals who were clinically diagnosed with acne vulgaris were selected for this cross-sectional analysis. The sample size thus reflects the total number of acne cases identified in the parent study, rather than a pre-calculated sample based on population estimates[16]. A dermatologist-trained, specialized medical team appraised the scarring and determined the severity of the acne. The dermatologist cross-validated this evaluation to guarantee the precision and dependability of the findings.

Acne severity was categorized into three groups – mild, moderate, and severe – based on clinical examination by a trained medical team. Acne scarring was graded using the ECCA grading scale, which classifies scarring into four categories:

Grade 1: Shallow scars covering <25% of the face, not visible from a distance.

Grade 2: Moderately deep scars affecting 25–50% of the face, mildly visible.

Grade 3: Deep, prominent scars involving >50% of the face, clearly visible.

Grade 4: Very deep and extensive scars, visible even from a distance.

All assessments were cross-validated by a certified dermatologist to ensure diagnostic consistency and grading accuracy.

Statistical analysis

Microsoft Excel was used to enter the gathered data, and any incorrect or inconsistent answers were eliminated after a thorough assessment. The statistical program SPSS (Statistical Package for the Social Sciences) version 16 was used to perform the analysis. This program was used to investigate the relationship between possible risk variables and acne manifestation. Given the limited number of participants with severe acne, moderate and severe cases were combined into a single category to enhance statistical power and ensure the robustness of the analysis. Similarly, acne scarring grades were consolidated by merging Grades 1 and 2, as well as Grades 3 and 4, due to small subgroup sizes, allowing for more reliable and interpretable comparisons. Sensitivity analyses using the original categories yielded similar patterns of association but with wider confidence intervals (CIs). Three age groups were established: those under the age of 19, those between the ages of 20 and 24, and those over 24. Multivariate adjustments were performed with gender as a covariate. Univariate analyses were initially conducted to explore associations between potential risk factors and acne severity. Bivariate comparisons were performed using chi-square tests to examine crude associations between individual variables (e.g., age, gender) and acne outcomes. For multivariate analysis, logistic regression models were constructed to assess the association between dietary habits and acne severity, adjusting for age, gender, family history of acne, fast food intake, and dairy consumption. Statistical significance was set at P < 0.05, and results were presented as odds ratios with 95% CIs.

Results

A total of 386 participants were included in the final analysis. The age distribution of the patients ranged from adolescents to adults, with a mean age of 22.7 years (SD ± 2.6). The mean age of the participants was 22.7 years (SD ± 2.6), and the majority were female (64.8%). A family history of acne in one parent was reported by 54.9% (n = 212) of participants, while 11.9% (n = 46) reported a history in both parents, suggesting a possible genetic predisposition (Table 1).

Table 1.

Association between acne severity grade and age, gender, family history, frequency of fast food intake, and dairy intake (n = 386)

Variables	Acne severity grade		COR (95%CI)	P-value
	Mild	Moderate/severe
Age (in years)
≤19	45 (32.80%)	92 (67.20%)	RC	0.03
20–24	54 (270%)	146 (73.00%)	1.26 (0.78–2.041)
>24	23 (46.90%)	26 (53.10%)	0.53 (0.27–1.04)
Gender
Male	41 (30.10%)	95 (69.90%)	RC	<0.0001
Female	81 (32.40%)	169 (67.60%)	2.31 (0.57–1.41)
Family history of acne
None	46 (35.90%)	82 (64.10%)	RC	0.43
Only one parent	62 (29.20%)	150 (70.80%)	1.35 (0.85–2.16)
Both parents	14 (30.40%)	32 (69.60%)	1.28 (0.62–2.64)
Fast food
Never/occasionally	23 (25.40%)	41 (64.10%)	RC	0.35
Once/twice a week	77 (27.50%)	186 (70.70%)	0.30 (0.76–2.40)
Most of all days	22 (25.40%)	37 (62.70%)	0.87 (0.45–1.96)
Dairy product
Never/occasionally	36 (27.10%)	94 (72.30%)	RC	0.20
Once/twice a week	41 (29.90%)	96 (70.10%)	0.89 (0.52–1.52)
Most of all days	45 (37.80%)	74 (62.20%)	0.63 (0.36–1.07)

COR, crude odds ratio; RC, reference category; CI, confidence interval.

In terms of acne severity, most participants had moderate acne (66.6%, n = 257), followed by mild acne (31.6%, n = 122). Severe acne was rare, observed in only 1.8% (n = 7) of participants. Regarding acne scarring, 26.4% (n = 102) had Grade 1 scarring (minimal), 65.3% (n = 252) had Grade 2 (mild), 6.7% (n = 26) had Grade 3 (moderate), and 1.6% (n = 6) had Grade 4 (severe) scarring.

Regarding dietary habits, 68.1% (n = 263) consumed fast food once or twice per week, 15.3% (n = 59) on most or all days, and 16.6% (n = 64) consumed it never or occasionally. Daily dairy consumption was reported by 30.8% (n = 119), weekly by 35.5% (n = 137), and occasional or none by 33.7% (n = 130). A majority of participants (82.6%, n = 319) reported no history of alcohol consumption, whereas 17.4% (n = 67) reported alcohol intake.

Regarding sibling history, 54.7% (n = 211) had no siblings with acne, one sibling was affected in 28.8% (n = 111), two siblings in 15.3% (n = 59), and three siblings in 1.3% (n = 5).

Relation of acne severity with age, gender, family history, frequency of fast-food intake, and dairy intake

Chi-square analysis showed that acne severity was significantly higher among males (P < 0.0001) and individuals under 19 years of age (P < 0.05). There was no significant association between acne severity and family history, fast food or dairy intake, alcohol use, or sibling acne history. Similarly, acne scar severity was significantly greater in males (P < 0.0001) but showed no significant association with age, family history, dietary factors, alcohol consumption, or sibling acne history (Table 2).

Table 2.

Association between acne scar grade and age, gender, family history, frequency of fast-food intake, and dairy intake

Variables	Acne scar grade		COR (95%CI)	P-value
	Grade 1/2	Grade3/4
Age (in years)
≤19	125 (91.20%)	12 (8.80%)	RC	0.53
20–24	182 (91.00%)	18 (9.00%)	1.03 (0.47–2.21)
>24	47 (95.50%)	2 (4.10%)	0.44 (0.96–2.05)
Gender
Male	126 (92.60%)	10 (7.40%)	RC	<0.0001
Female	228 (91.20%)	22 (8.80%)	1.21 (0.55–2.64)
Family history of acne
None	114 (89.10%)	14 (10.90%)	RC	0.41
Only one parent	197 (92.10%)	15 (7.10%)	0.62 (0.28–1.33)
Both parents	43 (93.50%)	3 (6.50%)	0.56 (0.15–2.07)
Fast food
Never/occasionally	59 (92.20%)	5 (7.80%)	RC	0.59
Once/twice a week	239 (90.90%)	24 (9.10%)	1.18 (0.43–3.23)
Most of all days	56 (94.90%)	3 (5.10%)	0.63 (0.14–2.77)
Dairy product
Never/occasionally	121 (93.10%)	9 (6.90%)	RC	0.77
Once/twice a week	125 (91.20%)	12 (8.80%)	1.29 (0.52–3.17)
Most of all days	108 (90.80%)	11 (9.20%)	1.36 (0.54–3.43)

COR, crude odds ratio; RC, reference category; CI, confidence interval.

Multivariate logistic regression analysis was performed to identify factors that are independently associated with acne severity and scarring. After adjusting for age, gender, family history of acne, fast food intake, and dairy consumption, none of the assessed variables were significantly associated with moderate/severe acne, as shown in Table 3. Similarly, in the study of acne scarring (Table 4), no independent associations were found with higher-grade scarring (Grade 3/4).

Table 3.

Multivariable logistic regression analysis of factors associated with acne severity

Variable	Categories	AOR (95% CI)	P-value
Age (in years)	≤19 (Ref)	–	–
	20–24	1.18 (0.70–1.99)	0.53
	>24	0.61 (0.29–1.27)	0.18
Gender	Male (Ref)	–	–
	Female	1.15 (0.66–2.01)	0.62
Family history	None (Ref)	–	–
	One parent	1.21 (0.73–2.00)	0.46
	Both parents	1.17 (0.55–2.50)	0.67
Fast food	Never/occasionally (Ref)	–	–
	Once/twice a week	1.20 (0.65–2.20)	0.55
	Most days	0.95 (0.45–2.03)	0.89
Dairy product	Never/occasionally (Ref)	–	–
	Once/twice a week	0.93 (0.52–1.67)	0.81
	Most days	0.72 (0.38–1.35)	0.31

AOR, adjusted odds ratio.

Table 4.

Multivariable logistic regression analysis of factors associated with acne scarring severity

Variable	Categories	AOR (95% CI)	P-value
Age (in years)	≤19 (Ref)	–	–
	20–24	1.01 (0.42–2.45)	0.98
	>24	0.52 (0.10–2.66)	0.44
Gender	Male (Ref)	–	–
	Female	1.32 (0.52–3.33)	0.56
Family history	None (Ref)	–	–
	One parent	0.71 (0.29–1.73)	0.46
	Both parents	0.62 (0.13–2.91)	0.54
Fast food	Never/occasionally (Ref)	–	–
	Once/twice a week	1.16 (0.39–3.42)	0.78
	Most days	0.71 (0.14–3.60)	0.68
Dairy product	Never/occasionally (Ref)	–	–
	Once/twice a week	1.26 (0.44–3.58)	0.67
	Most days	1.29 (0.45–3.75)	0.64

AOR, adjusted odds ratio.

Discussion

Our study shows that the majority of participants have acne scar grade 2 (65.20%) and moderate acne severity, which is 66.60%. Contrary to the initial hypothesis, the study findings suggest that the consumption of fast foods and dairy products does not have a significant association with the prevalence or severity of acne. These results challenge the commonly held belief that diet plays a substantial role in acne formation.

The potential relationship between dietary factors and the development of acne has been extensively investigated worldwide. However, findings have been inconsistent, likely due to variations in study design, methodologies, case definitions, study populations (including dietary habits and cultural differences), and outcome measures.

Despite these discrepancies, Meixiong et al[6] systematic analysis concluded that young individuals in countries like the US, Europe, and Australia, where a Western diet is prevalent, may see an increase in acne as a result of consuming more dairy products. On the other hand, dairy consumption seems to have no bearing on the occurrence of acne in young people in non-Western nations. Similarly, even after controlling for confounding variables such as age, age at menarche, body mass index (BMI), and total energy intake, Adebamowo et al^[17,18] identified a link between women’s acne and milk consumption, especially skim milk. Consistent findings were observed by Juhl et al[19], who demonstrated a similar association in adolescent boys and adults.

Our study underscores the importance of considering gender and age as significant factors in acne development. The findings reveal a clear association between gender and acne, with males exhibiting a higher prevalence of acne compared to females. This observation supports previous research indicating hormonal influences, such as increased androgen levels, as a contributing factor to acne in males[20]. The study also emphasizes the importance of age in determining the occurrence of acne. Acne was shown to be more common in younger people, which is consistent with the established link between adolescent hormonal shifts and acne development. During adolescence and early adulthood, increased androgen production – particularly testosterone and dihydrotestosterone – stimulates sebaceous gland activity and enhances sebum production, creating a favorable environment for the proliferation of Cutibacterium acnes and subsequent inflammation. This explains the higher acne prevalence in individuals below 20 years of age. Furthermore, males tend to experience more severe acne than females due to higher circulating androgen levels and larger, more active sebaceous glands[20].

Although dietary glycemic index (GI) and glycemic load are proposed mechanisms in acne pathogenesis[6], this study did not directly assess these parameters. As such, conclusions regarding their impact cannot be drawn. Our findings should therefore not be interpreted as a dismissal of their possible role in acne development.

In their comprehensive analysis of food and acne, Fajri et al[21] reported a significant positive association between fast food consumption and the incidence of acne vulgaris among college students. Similarly, Penso et al[22] identified a correlation between the intake of fatty and sugary foods, sugar-sweetened beverages, and milk with the presence of acne in adults. Fast food, salty snacks, and chocolate confections were found to be potential dietary factors that promote acne in a study by Rudzinska et al[23] among Polish female adolescents. On the other hand, it was proposed that dairy products other than milk could prevent acne.

In Nepal, traditional diets often include boiled milk, curd, lentils, rice, and ghee, while urban areas are experiencing a dietary shift toward Westernized fast foods such as deep-fried snacks, instant noodles, and sugar-sweetened beverages. Unlike processed Western dairy, Nepalese dairy is often unprocessed and locally sourced, which may differ in hormonal and glycemic impact. This distinction may explain the absence of significant dietary associations observed in our study compared to Western studies.

The lack of association observed in this study may be due in part to methodological differences from studies reporting positive associations^[21,22], including dietary data collection tools, definitions of fast food, and cultural dietary habits. Additionally, differences in genetic background, acne grading systems, and environmental exposures could explain discrepancies.

Although our study did not find a statistically significant association between fast food or dairy intake and acne severity, evidence from other Asian populations suggests that dietary components may still influence acne pathogenesis. In an Indian cohort, Nagaswetha et al[24] demonstrated that high GI and low dietary fiber intake were significantly associated with increased acne severity among young adults. Similarly, Pradad et al[25] reported that Indian adolescents adhering to a traditional, healthy dietary pattern exhibited significantly lower acne severity scores compared to those following a Westernized diet. These findings highlight the role of broader dietary patterns beyond individual food groups. In Thailand, Roengrithtidet et al[25] found that high intake of oily/fried foods and chocolate significantly increased acne severity, while consumption of sugar-free, milk-free tea and vegetables was protective. Our findings may reflect similar but subtler dietary influences, or could be limited by measurement constraints, such as the lack of portion size estimation and comprehensive dietary indices like glycemic load.

While our study shows the absence of a significant association between diet and acne, it is important to acknowledge the limitations of the study. The study’s sample may not be representative of the general population, particularly rural communities or adolescents not seeking dermatologic care, which limits the generalizability of the findings. The underrepresentation of males and the clinic-based sampling may reflect differential health-seeking behavior, introducing selection bias that limits the generalizability of our gender-based findings. The dietary assessment was based on self-reported frequency without validated portion size data or standardized food frequency questionnaire use, which may have introduced misclassification or recall bias. Convenience sampling may also have introduced selection bias. The study focused only on fast food and dairy consumption, neglecting other dietary factors such as sugar intake, processed food, and overall dietary quality that could contribute to acne development. The cross-sectional design prevents establishing causality and temporal relationships between diet and acne, as it provides a snapshot of data at a single point. Current dietary habits may not accurately reflect those during acne onset, and no data were collected on acne duration or age at first onset. Several unmeasured confounders may have influenced our findings. Variables such as BMI, glycemic load of the diet, total caloric intake, stress levels, hormonal profiles (e.g., PCOS), skincare routines, and socioeconomic status were not captured. These factors could impact both acne pathogenesis and dietary choices, thus confounding the observed associations.

Future research should consider incorporating prospective cohort designs that allow for the assessment of dietary exposures over time in relation to acne onset and progression. Employing more comprehensive methodologies to investigate the complex interactions between diet, gender, age, and acne is recommended. The use of a more granular intake scale and validated, culturally adapted food frequency questionnaire is recommended. By further exploring these relationships, a more nuanced understanding of the etiology of acne can be achieved.

Conclusion

The finding suggests that biological factors, such as hormonal fluctuations during adolescence and differences in sebum production, may have a more substantial impact on acne development than dietary factors. This study emphasizes the need for a multifaceted approach to acne research and management. Healthcare professionals should consider gender and age as crucial factors when evaluating and treating individuals with acne. While no statistically significant association was found between fast food or dairy intake and acne severity or scarring in this cohort, this does not rule out the potential influence of diet, especially considering methodological limitations and findings from other populations.

Ethical approval

None.

Consent

Written informed consent was obtained from the patient for publication and any accompanying images. A copy of the written consent is available for review by the Editor-in-Chief of this journal upon request.

Sources of funding

None.

Author contributions

BD, RB, and MB wrote the original manuscript, reviewed, and edited the original manuscript. SS, BS, BP, SB, RM, and SS reviewed and edited the original manuscript. All the authors read and approved the final manuscript.

Conflicts of interest disclosure

None.

Guarantor

Dr Bikrant Dhakal.

Research registration unique identifying number (UIN)

researchregistry11170.

Provenance and peer review

Not commissioned, externally peer-reviewed.

Data availability statement

All the required information are in the manuscript itself.

Acknowledgements

Not applicable.