Why pen starts leaking while coming up?

Pens can leak when ascending due to changes in air pressure and temperature, which can cause the ink inside to expand. If the pen is subjected to altitude changes, such as when flying, the internal pressure may drop, leading to ink being forced out of the nib. Additionally, if the pen is overfilled or if the seal is compromised, it increases the likelihood of leakage during such changes. Proper storage and handling can help mitigate this issue.