Deep dermatophytosis is the rarely reported occurrence of invasion of dermatophytes from the epidermis into the dermis and subcutaneous tissue. It is distinctive from Majocchi granuloma in that hair follicle invasion does not occur.

Deep dermatophytosis is reported almost exclusively in immunocompromised individuals. Iatrogenic immunosuppression (including in organ transplant patients and from chemotherapy), HIV disease, and diabetes (type 1, type 2) are important predisposing factors. Additionally, individuals with caspase recruitment domain family member 9 (CARD9) deficiency, a primary immunodeficiency disorder with compromised antifungal immunity, develop severe superficial and invasive fungal infections, including deep dermatophytosis. A chronic superficial dermatophyte infection is present is around two-thirds of all patients with deep dermatophytosis.

Males are more commonly affected (ratio of 2.4:1). Patients with CARD9 deficiency develop deep dermatophytosis in the first 4 decades of life, whereas those with acquired immunosuppression are older. Trichophyton rubrum was the causative organism in the majority of reported cases, with other Trichophyton species also reported.

Deep dermatophytosis typically presents as papules, plaques, or nodules. The lower extremities are the most commonly affected sites.