What does it mean if your cold sore is yellow?

If your cold sore is yellow, it is a sign that the sore has become infected. The infection can be caused by bacteria, such as Staphylococcus aureus or Streptococcus pyogenes, which can enter the sore through a break in the skin. Infected cold sores may appear yellow, crusty, and swollen, and may also be accompanied by pain, itching, and fever. If you think your cold sore is infected, it is important to see a doctor for treatment. Treatment may include antibiotics, antiviral medications, and pain relievers.