What causes tracheomalacia?

Weak tracheal cartil: Weakening of the cartilage "rings" along the front of the trachea, which causes the trachea to flatten ... Some consider invagination of the soft back wall of the trachea also as tracheomalacia ... I disagree, but effect is same, narrowing of the tracheal lumen and some difficulty breathing.

Uncommon: Tracheomalacia is collapse of the trachea (the windpipe) and is often confused with laryngomalacia which is collapse of the voicebox (which is above the trachea). Tracheomalacia is quite uncommon in infants except those with repaired t-e fistulas, and those with unrepaired vascular rings.