Blisters/rashes on feet can be caused by many things like allergic reaction, uncomfortable shoes, walking a long way. Sometimes sores on the body, particularly palms of the hands or feet, can be a sign of syphilis, an infection spread by sex. The ONLY way you can know if you have syphilis is to have a blood test, so go to your nearest clinic for this. Without treatment syphilis can affect your eyes, brain, heart and the rest of your body, so seek proper medical help soon if you are worried.
Attribution: Straight Talk Foundation & Marie Stopes