Your academic record is the most important part of your college application, so it's common to be concerned about that rogue 'C' on your transcript or that one semester when the grades took a nosedive. At some of the country's most selective colleges, a few bad grades could indeed be the difference between an acceptance letter and a rejection.
But what if the low grades were the result of circumstances out of your control? Should you explain the situation in your college applications?
There are many situations in which an explanation of your grades is not appropriate and might come across as sounding desperate. College admissions officers aren't interested in hearing about the one test you bombed because of the flu, the semester your grades dropped because your love life was in turmoil, or that mean teacher who never gave you a break.
When you have a serious disruption in your life, however, a note of explanation could be a good idea. For information on when you should and shouldn't explain bad grades, and to learn the best route for getting the information to the admissions office, read this article on explaining bad grades.