According to WebMD, doctors believe ringworm is contagious for 24 to 48 hours once treatment has started. Without treatment the individual continues to be contagious to anyone who comes in contact with him or a personal item he has used or touched.
MedicineNet shares that ringworm is typically transmitted by human-to-human contact, especially skin-to-skin contact. It can also be transmitted by sharing personal items, such as combs, brushes or clothing. Also, coming into contact with locker rooms or pool surfaces that harbor ringworm can cause an infection of ringworm. Dogs, cats and other pets can also transmit the infection to humans.