Objective Seborrheic dermatitis (SD) is a chronic inflammatory disease. The etiology of the disease is still unknown. The systemic immune-inflammation index (SII), red cell distribution width (RDW), mean platelet volume (MPV), C-reactive protein (CRP), monocyte to HDL cholesterol ratio (MHR), platelet to lymphocyte ratio (PLR), and neutrophil to lymphocyte ratio (NLR) have all been reported as inflammatory markers in recent studies. However, these inflammatory markers have not been explored in SD patients. This study aimed to explore inflammatory and hematological parameters in SD patients with healthy controls (HCs) and evaluate their possible relationship with disease severity. Materials and Methods One hundred patients who presented to our hospital were diagnosed with SD and 74 HCs were retrospectively included in our study. The seborrheic dermatitis area severity index (SDASI) score was used to assess the severity of the SD. Results The patient group's mean PLR, MPV ve CRP levels were statistically significantly higher than the HCs (p < 0.05). There was no statistically significant difference in the patients compared with the control group regarding RDW, NLR, MHR, and SII levels (p > 0.05). There was no statistically significant correlation between NLR, PLR, MPV, monocyte/HDL cholesterol, SII levels with age, and SDASI in the patient group. There was a significant correlation between CRP with age and RDW with SDASI score. Conclusion Hematological parameters and CRP are low-cost tests. These tests can be used to define inflammation levels in inflammatory diseases. This study shows that PLR, CRP, and MPV may be used as novel inflammatory markers in SD.