Sweaty feet make blisters more likely. Blisters are a common occurrence, and most people will experience them at some point in their life. They often appear after walking or running for long periods of time, especially if the feet have become sweaty or when wearing shoes that do not fit correctly. Blisters are raised fluid-filled pockets and not generally a serious concern. It is best not to burst blisters, letting them heal on their own. Applying a bandage can provide relief. If blisters occur regularly alongside flu-like symptoms, speak with a doctor.