A blister is a small pocket of fluid that forms between the upper layers of the skin. It usually occurs as a result of friction, burns, or irritation, and can be filled with clear fluid, blood, or pus. Blisters serve as a protective barrier, helping to shield the underlying skin from further damage while it heals. Common causes of blisters include wearing ill-fitting shoes, sunburn, or allergic reactions. While most blisters heal on their own, it is important to avoid popping them, as this can lead to infection. Proper care and protection can help ensure a smooth recovery.