I'm with you... I never re-used the pen needles... after insurance, it's just too cheap to re-use. Also, leaving the needle on the pen between uses leaves a path open into the insulin for either contamination or leakage. I know many people re-use without a problem, but for me it's just not worth it.
Great question. This reasoning makes a lot of sense .
Consider the type of things that goes in a fridge( meats and veggies harbor some nasty bugs) and people who forget to wash their hands when touching compromised surfaces might touch the in use pen when removing it. They might wash their hands when putting on a new needle but either hand could have touched the outside of pen and hand(s) are no longer clean.
I guess reason for not storing used needle on pen you have just used might allow microbes to travel up the needle and contaminate the entire pen. This is assuming patient didn’t rub the alcohol wipe for 30S or more and let alcohol, air dry completely. Also I assume the insulin doesn’t have fungicides or antibiotics mixed into its formulation.
I only thought it had to do with the degrading of the Lantus insulin because of the warm cold continuous cycling for in use pens not stored at room temperature.
Then read a recent article regarding Lantus kept at high temoeratures(37 C) in Thai households without AC with no significant degradation of potency. So the actual reasoning behind storage temps was ambiguous for some time.