What causes brown spots inside the skin on the soles of the feet, and what should be done about it?

Generally, brown spots on the sole of the foot may be caused by factors such as hyperpigmentation, callus pigmentation due to friction, pigmented nevi, flat warts, or stasis dermatitis. Depending on the specific situation, improvements can be made through general care, medication, or physical treatments. Detailed analysis is as follows:

1. Hyperpigmentation

Prolonged sun exposure, contact with chemicals, or post-inflammatory conditions can lead to increased activity and accumulation of melanocytes in localized areas. Protect feet from sunlight, avoid irritants, and consume more fresh fruits and vegetables rich in vitamin C.

2. Callus Pigmentation Due to Friction

Long periods of walking or wearing hard shoes cause thickening of the stratum corneum on the soles, leading to pigment deposition under repeated friction. Switch to soft, breathable footwear and socks; soak feet in warm water every night and gently exfoliate dead skin using a pumice stone.

3. Pigmented Nevus (Mole)

Formed by benign proliferation and clustering of melanocytes, these can appear within the skin of the sole and typically have clear borders. Avoid chronic friction or irritation. If stable, monitor regularly; if treatment is needed, options include carbon dioxide laser therapy, liquid nitrogen cryotherapy, or surgical excision.

4. Flat Warts

Caused by human papillomavirus (HPV) infection, resulting in abnormal keratinocyte proliferation. Lesions have rough surfaces and may appear brown. Keep feet clean and dry, avoid scratching, and apply topical medications as prescribed—such as tretinoin cream, imiquimod cream, or fluorouracil ointment.

5. Stasis Dermatitis

Impaired venous return in the lower limbs leads to blood pooling and skin hypoxia, causing hyperpigmentation and brownish spots. Avoid prolonged standing or sitting, elevate legs during rest, and take medications as directed—such as micronized purified flavonoid fraction (MPFF), calcium dobesilate capsules, or diosmin tablets.

Maintain proper foot care: wear well-fitting shoes and socks to reduce friction; practice good foot hygiene to prevent viral infections; engage in moderate physical activity to promote circulation in the lower limbs. Seek medical evaluation promptly if spots rapidly enlarge, become irregular in shape, or are accompanied by itching or pain.