Tinea pedis (Athlete's foot): This is a common fungal infection that can cause brown discoloration on the bottom of the foot, especially in the areas between the toes and on the soles. It's often accompanied by itching, scaling, and sometimes blistering.

Eczema (Dyshidrotic eczema): This condition can lead to brown discoloration due to chronic inflammation and pigmentation changes. It's characterized by small, itchy blisters on the soles of the feet.
Hyperpigmentation due to friction or pressure: Repeated friction or pressure on the skin of the foot, such as from poorly fitting shoes, can cause brown discoloration.
Melanotic macules: These are benign growths that can appear as brown spots on the soles of the feet, often due to an increase in melanin.

Malignant melanoma: Although rare, melanoma can present as a new or changing brown spot on the foot. Given its potential lethality, it's crucial to consider and rule out this diagnosis, especially if the discoloration is asymmetric, has irregular borders, color variation, or is larger in diameter.
Diabetic foot ulcers with secondary infection: In patients with diabetes, foot ulcers can become infected, leading to discoloration. Early recognition and treatment are critical to prevent serious complications.

Argyria: A condition caused by exposure to silver or silver compounds, leading to blue-gray pigmentation of the skin, which might appear brown in certain lighting conditions.
Chromoblastomycosis: A rare fungal infection that can cause brown to black lesions on the skin, typically found in tropical regions.
Minocycline-induced hyperpigmentation: A side effect of long-term minocycline use, which can cause blue-gray or brown discoloration in various parts of the body, including the feet.