What can cause pain in my outer foot arch?

Many causes: Sprain, plantar fasciatis, stress fracture are a few.Go see a podiatrist.

There are a few: Things. Knowing your foot type would be helpful or knowing precisely where on the outer foot it hurts. On the top? Bottom? Side? Type of pain you feel? Without this info anything from tendonitis to neuritis, avulsion fracture of the 5th met, plantar fascitis can be a cause. A foot doc should be able to help you with an in person evaluation.

Many possibilities: Your pain could due to trauma (fracture, sprain, arthritis, inflammation), infection, metabolic conditions (gout), poor circulation, musculoskeletal or biomechanical abnormality and different neurologic conditions (neuropathy). A thorough history and physical exam and possibly some laboratory and radiology exams are needed to determine the exact cause. The treatment varies depending on the cause.