There are several causes of pain on the outside of the foot: 1. Plantar tendinitis: The starting point of the plantar tendon membrane is in the heel bone, and the termination point is at the base of the toe bone. If you often walk with weight, walk up and down stairs, hike, walk with a burden, walk with a backpack, or perform heavy physical exercise, it can cause an increase in the load on the plantar tendon membrane. If a tear or inflammation occurs on the lateral side of the plantar tendon membrane, it will mainly manifest as pain on the lateral side of the foot. 2, peroneal tendonitis: especially if inflammation occurs at the connection between the short fibular muscle and the fifth metatarsal ridge, it will manifest as pain on the lateral side of the foot. This is mainly due to repeated foot inversion activities, caused by tendon stretching, over time will appear tendonitis, and sometimes even the fifth metatarsal base of the bone fracture, so there will be pain in this area.