Mycosis fungoides is a type of skin cancer that initially becomes apparent as a red rash on the individual's skin, according to the National Cancer Institute. In the infection's final phase, tumors form and become apparent on the skin.
Mycosis fungoides occurs in four phases: the premycotic phase, the patch phase, the plaque phase and the tumor phase. In the premycotic phase, a scaly red rash forms on an area of the skin that has not necessarily been exposed to sunlight. In the patch phase, the rash is even redder with an eczema-like texture. In the plaque phase, the bumps of the rash are raised and may form hardened lesions on the skin. In the tumor phase, tumors become evident on the skin and may cause ulcers or infection, notes the National Cancer Institute.