Answered 12/12/2014 by Samuel Grossman, BS Pharm, Pharm.D, CDE
Insulin vials and pens are sensitive to heat and cold. If you are outdoors, make sure the insulin is well covered on under clothing without direct exposure to cold. When traveling, make sure you keep the insulin pen or vial on person with you as oppose to leaving it in your checked in bag when you travel by plane. Cold temperature in the baggage area may freeze your insulin. Keep insulin vial or pen in an insulated casing and check on it periodically. Very cold, frozen, or overheated insulin may turn a clear solution cloudy or have visible crystals.