Sinus infection mucus is typically yellow or green, though it can also appear white or cloudy. The color comes from white blood cells your immune system sends to fight the infection. As those cells pile up and die off, your nasal discharge shifts from clear to progressively darker shades.
What Each Mucus Color Means
Clear mucus is normal. It’s mostly water mixed with proteins, antibodies, and dissolved salts. Allergies can increase the volume of clear mucus, but the color itself isn’t a sign of infection.
White or cloudy mucus signals congestion. Swollen, inflamed tissue inside your nose slows the flow of mucus, causing it to lose moisture and turn thick and opaque. This is often the first shift you notice at the start of a cold or sinus infection.
Yellow mucus means your immune response is ramping up. White blood cells rush to the site of infection, do their work, and get swept out in the mucus. That yellowish tinge is essentially the debris from that battle. Most colds produce yellow mucus at some point, so yellow alone doesn’t confirm a sinus infection.
Green mucus appears when the fight intensifies. Your discharge becomes thick with dead white blood cells, and an iron-containing enzyme inside those cells gives the mucus its distinctly green hue. (That enzyme was originally named “verdoperoxidase” because of its vivid green color.) Green mucus looks alarming, but it’s a sign your body is working hard, not necessarily that you need antibiotics.
Green Mucus Doesn’t Always Mean Bacterial
This is the most common misunderstanding about mucus color. Many people assume green means bacterial infection, while yellow means viral. That’s not reliable. Viral sinus infections routinely produce green mucus, especially around days three through five of a cold. Clinical research confirms that mucus color alone is a poor predictor of whether bacteria are actually involved. In one study, patient-reported mucus color had only 39% specificity for identifying bacterial infection, meaning it was wrong more often than it was right.
Doctors don’t diagnose bacterial sinusitis based on color. Instead, they look at the timeline and pattern of your symptoms. According to guidelines from the Infectious Diseases Society of America, a bacterial sinus infection is likely if:
- Symptoms persist 10 days or more without any improvement.
- Severe symptoms appear early: a fever of 102°F or higher with facial pain and nasal discharge lasting three to four days.
- Symptoms double-dip: you start to feel better after four to seven days, then get noticeably worse again.
If none of those patterns apply, your body is most likely fighting off a virus, and antibiotics won’t help regardless of how green the mucus is.
How Sinus Infections Are Officially Defined
The American Academy of Otolaryngology defines acute sinusitis as up to four weeks of cloudy or colored (not clear) nasal drainage, plus at least one of these: nasal congestion or stuffiness, or pain, pressure, and fullness in the face, head, or around the eyes. Color matters in this definition only in that the discharge is no longer clear. Beyond that threshold, the shade of yellow or green doesn’t change the diagnosis.
What About Red, Brown, or Black Mucus?
Pink or red-streaked mucus usually means a small blood vessel in your nose has burst. This is common when your nasal passages are dry, irritated from frequent blowing, or inflamed from an ongoing infection. It’s not typically dangerous on its own.
Brown mucus can result from inhaling smoke, pollution, or dust. It can also appear when old blood mixes with nasal discharge. Smokers see brown mucus more frequently.
Black mucus is rare and warrants attention. It can come from inhaling heavy soot or environmental contaminants, but it can also signal a serious fungal infection, particularly in people with weakened immune systems.
What to Watch For Beyond Color
Pay more attention to how long your symptoms last and how they evolve than to the exact shade of your mucus. A typical viral sinus infection peaks around days three to five and gradually improves over seven to ten days. If you’re still feeling the same (or worse) at the ten-day mark, that’s the clearest signal something more than a virus is going on.
Certain symptoms suggest the infection has become serious enough to need immediate care: a fever above 103°F, swelling or pain around the eyes, vision changes, a stiff neck, confusion, or seizures. These can indicate the infection is spreading beyond the sinuses, and they call for emergency evaluation rather than a wait-and-see approach.