India, Oct. 4 -- You have probably used hundreds of pens in your lifetime without giving much thought to their caps. But look closely at a typical ballpoint pen and you may notice a tiny hole at the top of the cap.

It might appear to be a minor design detail, or perhaps something added to make the cap look less airtight. In reality, the opening is connected to an important safety consideration that has shaped the design of pen caps over the years. (Also read: Everyday Explained: Why are piano keys black and white? Know the fascinating history, math and design behind the pattern )

So, why is there a hole in your pen cap? Let's find out.

The opening in many pen caps is designed to allow air to pass through the cap, helping reduce the ris...