Why Ballpoints Leak (And What To Do) 

If you’ve ever experienced an unexpected ink stain on your shirt or trousers, you may be wondering what had caused your ballpoint to leak ink like that in the first place. Or you may have been writing and suddenly noticed that your hand is covered in steaks of leaked ink. Why is it that some ballpoint pens leak ink?

Common factors for leaking ballpoints are high temperatures, incorrect storing or positioning of the pen, capillary action, changes in air pressure, damage to the pen’s tip, or manufacturer’s defects. Leaking can be prevented by ensuring that the pens are stored correctly and used as instructed.

Although ballpoint pens have a good reputation and don’t tend to be leaky and messy, we sometimes do things that can increase the risk of leaking. We have summarized a few of these reasons below. 

What Causes A Ballpoint Pen To Leak? 

Compared to other types of pens like, e.g., gel pens, rollerball pens, and fountain pens, ballpoint pens are usually the least prone to leaking ink. However, certain factors can cause the ink to flow more freely. Next thing you know, your clothes or hands are stained with ink. 

1. Ballpoint Pen Leaking Caused By High Temperatures

Many of us like carrying our pens in a pocket for easy access when we need to use them. The problem is that body heat can cause the pen to leak. 

Our normal body temperature is high enough to cause ink molecules to liquefy or expand. When this happens, the ink will move to the tip or the bottom of the pen and leak out.

Ballpoint pens can also leak inside a bag if left in a warm car or outside in the sunlight for too long. It’s best not to leave your ballpoint pens in places where the temperature is above room temperature.  

2. Ballpoint Pen Leaking Caused By Incorrect Storing 

Ballpoint pens have caps for a reason. You guessed it – to prevent ink from getting on surrounding items or leaking out of the pen when there’s friction, especially if you’re traveling or moving around with the pens in your bag or pocket. 

If you’re throwing your pens into your pen case or pocket without the caps on, then expect to see ink stains and pen marks on the fabric. An exposed pen tip will mess ink on anything it touches. The caps are also meant to keep air out of the ink cartridge so that the ink won’t leak out when air enters the cartridge. 

The same goes for a retractable pen. Capping or retracting the pen’s tip will ensure no messy ink leaks ruin your favorite outfit or pen case. 

3. Ballpoint Pen Leaking Caused By Incorrect Positioning

Gravity is not on your side when it comes to storing and positioning your ballpoint pens correctly. If you’re storing your pens in a vertical position with the nib facing downwards, you’re asking for trouble. Gravity will pull the ink down toward the tip, and the possibility of ink leaking out from the tip is high. 

The above is especially true if you’re not using the pen for some time. The longer you leave the 

pen in the wrong position, the more ink will leak out. 

Using a pen at a strange angle, e.g., writing on a wall calendar can also cause the ink to leak. When you use the pen at an “upward” angle, you’re letting too much air rapidly enter the pen’s tip. This air can cause the ink to flow backward and leak out of the cartridge.  

4. Ballpoint Pen Leaking Caused By Changes In Air Pressure 

When you’re flying on a plane, changes in air pressure can cause your ballpoint pen to leak ink. The problem isn’t with the pen itself but rather with the air that gets trapped inside the pen’s ink cartridge. 

Liquids like pen ink do not expand or compress. When the pressure inside the cartridge equalizes with the surrounding air pressure in the cabin, it causes the air inside the cartridge to expand. When this happens, it can cause the ink inside the cartridge to be pushed out of the cartridge and leak out of the pen. 

5. Ballpoint Pen Leaking Caused By Capillary Action

Ballpoint pens work by capillary action, which refers to a phenomenon where ink flows out of the pen without the force of gravity. This is due to surface tension when the pen tip touches a water-absorbent fabric or surface. Ink gets pulled out of the ink cartridge and pen tip and is forced onto the surface it touches. 

Capillary action can cause the ink to leak out of the tip, regardless of the direction the pen’s tip is pointing. Therefore, leaking can occur even if the nib points upwards in your pocket or bag. 

6. Ballpoint Pen Leaking Caused By A Damaged Pen Tip

If you’ve ever analyzed the tip of a ballpoint pen closely, you would’ve seen that it has a very delicate structure that’s necessary for the pen to function properly. 

Naturally, if you drop the pen or use it for something other than writing, chances are you’re going to ruin the tip. The pen’s tip can also get scratched over time, especially if you use the pen often and use hard pressure when writing. A deformed or damaged tip won’t hold the ink in as it should, and ink will leak out or come out in thick streaks when you’re writing. 

7. Ballpoint Pen Leaking Caused By Manufacturing Defects 

If you’re buying from a cheap manufacturer, you may have problems with leaking ballpoint pens. For a ballpoint pen to function properly, you want the nib opening, ball diameter, and ink viscosity to balance. 

E.g., if you have a pen that uses low-viscosity ink with a ball diameter too small for a larger nib opening, then the pen will leak ink from the pen’s tip, and you will have very smudgy writing. 

Manufacturing defects are often out of our control, so ensure that you buy pens from reputable brands. 

What To Do If Your Ballpoint Pen Leaks Ink

There are a few things you can do to avoid leaking ballpoint pens and ink stains on your clothes, hands, books, and bags. We’ve listed a few tips below:

  1. Do not keep your ballpoint pen in your pockets – always store your pens in cool places, away from sunlight and body heat. 
  2. Always replace the pen’s cap and/or retract the pen’s tip after using the pen to avoid ink leaking out due to capillary action or friction. 
  3. Always store your pens in a holder with the tip facing upwards or in a pen case with the pen laying horizontally. 
  4. When flying on a plane, keep your pens stored in a Ziploc bag to avoid problems with the changes in air pressure
  5. Check the pen’s tip for damage or manufacturer defects before use, and discard if you suspect the tip is scratched or deformed. 


Ballpoint pens need care and maintenance, just like most other things that we use daily. Some factors that cause leaking are outside of our control, but most of them can be avoided by giving special attention to how we store and use our pens. If you heed the above information and follow our tips, then leaking ballpoint pens will be a thing of the past! 

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