Increasing redness around the blister
Warmth around the area
Swelling that is getting worse
Pain that is worsening instead of improving
Pus or cloudy drainage
Yellow, green, or foul-smelling fluid
Red streaks spreading from the blister
Skin around the blister becoming hard or very tender
Fever or chills
The blister not healing or getting bigger
The area becoming more swollen after being opened
Trouble moving the affected area because of pain or swelling