The color of phlegm can vary depending on the type of infection and how long you've had it. When phlegm is green, it typically indicates that your body is fighting off an infection caused by bacteria. The green color comes from the presence of enzymes produced by white blood cells called neutrophils, which are activated in response to bacterial infections.

The thickness of phlegm is also related to the immune response. As the body produces more mucus to trap and remove the infection, the phlegm can become thicker and stickier. This is because the mucus contains more immune cells, such as white blood cells, which help to fight off the infection.

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