Hemosiderin staining usually happens on the lower leg, near the ankles, or on your feet. It’s caused by blood leaking out of the tiny vessels called capillaries. The blood pools under the skin and leave a residue of hemoglobin that settles in the tissue there. Hemoglobin contains iron, which causes the rusty color of the stains.

Generally, two conditions can cause dark spots on the bottom or top of your feet: venous stasis dermatitis and malignant melanomas. Both of these conditions can cause discolored spots and other symptoms like pain and swelling to the foot and ankle.

Writing on her website, Dr. Angela Drury, DPM, FACFAS states that pigmentations on the feet are usually moles or freckles, but pigmentations may be cancerous lesions. According to Drury, two types of skin cancer can occur on the foot: melanoma and the precancerous condition actinic keratosis.