Kaposi's Sarcoma lesions occur most commonly on the soles of the feet They are irregular in shape and have a purplish, reddish or bluish black appearance. They tend to spread and form large plaques or become nodular. The nodular lesions have a firm rubbery appearance. The appearance of these lesions is an ominous sign. In the late 1970's and early 1980's an outbreak of Kaposi's sarcoma occurred in San Francisco, California. It was later learned that the disease was associated with AIDS infection. It can occur without the concurrent AIDS infection but this is very rare.
Chronic athlete's foot can cause an increased pigmentation to the bottom of the foot. It is associated with dry scaling skin and may have a reddish appearance.