Hello   This is a good question!  First of all here is our information page about sunscreen.   I think it depends more on how long the sunscreen lasts without wearing off.  If you are active outside despite the colder temps...you are going to sweat and therefore will need to reapply because the sunscreen has worn off.    Most of the literature recommends that you reapply your sunscreen every two to three hours even during winter.   In a Health Day report entitled, "Winter Sun Warrants Sunscreen" the author quotes a dermatologist who says:   "Often, winter sports are associated with higher elevations and reflection of ultraviolet light off the snow," said Dr. Elizabeth Tanzi, an assistant professor of dermatology at Johns Hopkins Hospital in Baltimore and a dermatologist in Washington, D.C. Think like you would at the beach, she said, even if the temperature is below zero. Use sunscreen of at least an SPF (sun protection factor) of 30, and reapply it every two or three hours.   This would be a good question for your doctor or dermatologist but it seems the advice on how often to reapply still holds the same for the winter months.    Hope this helps.  Thanks for your question!