Most people will never know

The opening in many pen caps is primarily a safety feature. If a cap becomes lodged in someone’s airway, a ventilation hole may allow some air to pass through, potentially reducing the risk of suffocation while help arrives. That matters especially for children, who may put small objects in their mouths. But the hole does not make a cap safe to chew or swallow, and it cannot guarantee breathing. A suspected airway blockage requires immediate emergency assistance.

Caps themselves evolved to protect writing tips and, depending on the design, help keep ink from drying out. Ventilation adds another consideration: protecting the person using the pen. Although holes are sometimes credited with improving ink flow or cutting manufacturing costs, those explanations are not universal and should not overshadow their established safety role. The practical lesson is simple: keep loose caps away from young children, discourage chewing, and never mistake this safeguard for complete protection.