- Chest trauma, such as from a car accident
- Repetitive trauma or overuse such as lifting weights/working out
- Viral infections, especially upper respiratory infections
- You can be genetically disposed to it
- Pregnancy
- Celiac Disease
- Candida
- You are NOT alone, this is a common condition, but NOT commonly diagnosed correctly
If you got Costo another way than what I listed, please leave a comment and I'll add it here. Thanks!