Association between serum zinc levels and seborrheic dermatitis: a systematic review and meta-analysis

Seborrheic dermatitis (SD), a chronic inflammatory condition, affects approximately 4.4% of the global population. Zinc regulates epidermal integrity, inflammation and immune function, yet its role in SD remains contested. To compare serum zinc concentrations between SD patients and healthy controls. PubMed/MEDLINE, Web of Science, Cochrane CENTRAL, OpenAlex and Google Scholar were searched from inception to April 2026. Pooled mean differences (MD) were calculated using a random-effects model with REML estimation and Hartung–Knapp correction. Subgroup analyses were performed by geographic region. Quality of included studies was evaluated using the JBI checklist and certainty of evidence was assessed using the GRADE approach. Six studies (n = 787; 406 patients with SD and 381 controls) were included. Serum zinc levels were lower in patients with SD compared with controls, but the pooled effect was not statistically significant (MD = − 3.63 µg/dL; 95% CI − 8.81 to 1.56; p = 0.1323), with moderate heterogeneity (I 2 = 34.9%). Subgroup analyses by geographic region showed a similar direction of effect in Iranian (MD = − 5.26 µg/dL; 95% CI − 37.28 to 26.76) and Turkish studies (MD = − 2.20 µg/dL; 95% CI − 16.91 to 12.51), while the Bangladeshi study showed an opposite trend (MD = 12.20 µg/dL; 95% CI − 15.66 to 40.06). No differences were observed across subgroups (p = 0.4023). The certainty of evidence was rated as low using the GRADE approach. Serum zinc levels appeared lower in patients with SD compared to healthy controls, though the certainty of this finding was limited. Whether this finding reflects a true biological relationship remains unclear. Studies that track zinc status over time and relate it to actual changes in disease activity are needed before any firm conclusions can be drawn.