Which skin condition is mainly caused by a fungal infection?

Ringworm is primarily caused by a fungal infection, specifically by dermatophytes, which are fungi that thrive on keratin found in skin, hair, and nails. The condition is characterized by circular, red patches with clearer centers, resembling a worm under the skin, hence the name "ringworm."

In contrast, verrucas, commonly known as warts, are caused by human papillomavirus (HPV) and are not fungal in nature. Psoriasis is an autoimmune skin condition that speeds up the life cycle of skin cells, leading to scaling and inflammation. Eczema, also known as atopic dermatitis, is primarily linked to genetics and environmental factors, resulting in itchy and inflamed skin rather than being caused by a fungal agent. This distinction makes ringworm the correct answer in this context.