The presence of bacterial infections can change the color of mucus, as reported by Cleveland Clinic. Mucus also changes color when the immune system is working to fight off an infection. Straight mucus contains proteins, water, antibodies and dissolved salts.
The color of mucus is a strong indicator of nasal health, as stated by Cleveland Clinic. For example, clear mucus indicates normal health, whereas white mucus indicates congestion from swollen or inflamed tissues in the nose. People with yellow mucus are often in the beginning stages of an infection, such as a cold or bacterial infection. Mucus changes from a clear or white color to yellow when infection-fighting cells travel to a microbial infection.
Mucus changes to a green color when the immune system is fighting off an infection in the body, according to Cleveland Clinic. Green mucus is thick with dead, white blood cells. People with green mucus who feel nauseous or have a fever should see a doctor. Pink or red mucus typically indicates the presence of blood resulting from a nose bleed or injury. Black mucus is common in individuals who smoke or use illegal drugs, and can also indicate the presence of a serious fungal infection.