Condensation forms on your lens when you have dramatic temperature and/or humidity changes and your camera is not protected from the elements. When your gear hits that dramatic change of air, condensation forms while the temperature regulates….which can definitely be worrisome on your expensive gear.
Don’t panic! A few rounds of condensation won’t ruin your camera, nor will your lens fogging up cause any permanent damage. However, you should definitely take some easy steps to prevent this from becoming a habit. Too many cycles can begin to wear on your gear, especially on the internal mechanisms.