BACKGROUND: Psoriasis is an immune-mediated skin disease with a chronic relapsing-remitting course. Hyperglycemia has been shown to correlate with psoriasis severity. However, whether it could trigger psoriasis flares is not known. OBJECTIVE: To investigate the association between hyperglycemia and psoriasis exacerbation. METHODS: We conducted a retrospective cohort study at a university-affiliated hospital in Bangkok, Thailand, between 2008 and 2022 to examine the effects of elevated HbA1c on psoriasis flares. Patients with psoriasis vulgaris and either type 2 diabetes mellitus (T2DM) or impaired fasting glucose (IFG) who had at least 2 HbA1c values were identified. Statistical analyses were performed using mixed-effects logistic regression. RESULTS: A total of 201 psoriasis patients (95 with severe psoriasis and 106 with mild psoriasis) with 1,717 follow-up visits were included in the analysis. In patients with severe psoriasis, HbA1c ≥ 7% (adjusted odds ratio (OR): 1.905 (95% confidence interval: 1.328-2.731)) and alcohol consumption status (adjusted OR: 3.328 (1.235-8.965)) were identified as independent prognostic factors for psoriasis flares. Meanwhile, in mild psoriasis patients, none of the variables were independently associated with psoriasis flares. CONCLUSION: Hyperglycemia and alcohol consumption were associated with exacerbation in patients with severe psoriasis who had T2DM/IFG.