Tinea corporis is a common dermatophyte infection, frequently transmitted through contact with infected animals. When treated inappropriately with corticosteroids, its classical features may be masked, resulting in tinea corporis incognito. In primary care, distinguishing steroid-modified infections from chronic inflammatory dermatoses is essential to avoid diagnostic delay.A 27-year-old female pharmacist with a known history of psoriasis presented with widespread annular plaques on the trunk and extremities. Notably, she reported no pruritus. She had self-administered oral methylprednisolone (16 mg/day) for presumed psoriasis flare. One week before symptom onset, she had adopted a stray cat. Physical examination revealed erythematous plaques with atypical morphology. Given treatment failure and exposure history, fungal infection was suspected. Mycological assessment supported tinea corporis incognito. Systemic corticosteroids were discontinued, and oral terbinafine (250 mg/day for 28 days) with topical luliconazole was initiated, resulting in complete clinical resolution.This case highlights the “healthcare professional–patient paradox,” where self-diagnosis and inappropriate steroid use masked a zoonotic infection, delaying correct diagnosis.Family physicians should maintain diagnostic vigilance when chronic skin diseases present atypically or fail to respond to immunosuppressive therapy. Detailed environmental and exposure history is crucial.Systemic corticosteroids suppress inflammatory responses, eliminating hallmark symptoms such as pruritus and altering lesion morphology. In patients with known dermatologic disease, new or changing patterns should prompt reconsideration of the diagnosis. Primary care continuity enables critical reassessment beyond prior labels.Tinea corporis incognito should be considered when presumed inflammatory dermatoses worsen under corticosteroid therapy. Family physicians play a key role in recognizing masked infections through holistic assessment and continuity of care.