When a cold turns yellow or green and drags on, many parents wonder about a sinus infection. Mucus color turns out to be a weaker clue than most people expect.

Why It Happens

The sinuses are air spaces in the facial bones connected to the nose by narrow channels. Viral colds or allergies can swell the lining and block those channels, letting fluid pool and sometimes allowing bacteria to grow. The American Academy of Pediatrics guideline covers acute bacterial sinusitis in children aged 1 to 18 and treats most runny noses and coughs as viral upper respiratory infections, with only a minority progressing to bacterial disease. The CDC likewise explains that antibiotics are needed only when the cause is bacterial.

What Patterns Raise Suspicion

The AAP guideline describes three ways to diagnose bacterial sinusitis:

  • Persistent illness: nasal discharge of any quality, or daytime cough, lasting more than 10 days without improvement. The wording “any quality” matters, because green color by itself does not make an infection bacterial.
  • Worsening illness: new or worsening discharge, daytime cough, or fever after the child had started to improve (a “double sickening”).
  • Severe onset: high fever together with thick nasal discharge for several days in a row. A typical cold tends to improve within 7 to 10 days, which is why day 10 is a useful checkpoint.

Care at Home

  • Keep a symptom log with start dates and changes; the timeline is the most useful thing to bring to the visit.
  • Offer plenty of fluids, which can thin secretions.
  • Use saline spray or rinses to loosen mucus.
  • Keep indoor air comfortably humid and smoke-free.
  • Give fever or pain medicine at the dose for age and weight if the child is uncomfortable.

Common Misunderstandings

  • “Green means antibiotics.” Color can change during an ordinary viral cold.
  • “We need an X-ray or CT.” The AAP guideline advises against imaging to diagnose uncomplicated sinusitis and reserves contrast CT for suspected eye or brain complications.
  • “Antibiotics work instantly.” The guideline suggests rechecking the child if there is no improvement within 72 hours or if symptoms worsen.
  • “Any runny nose past 10 days is sinusitis.” Allergic rhinitis and other causes can look similar, which is why a visit helps.

When to Seek Care

Call the pediatrician if nasal discharge or cough lasts more than 10 days without improvement, or if fever and symptoms return after getting better. For persistent illness the guideline allows either starting an antibiotic or watching for 3 more days; for worsening or severe illness it recommends an antibiotic, with amoxicillin (with or without clavulanate) as the usual first choice. Go to the emergency room right away for swelling or redness around the eyes that lasts all day, severe headache with neck pain, repeated vomiting, or unusual drowsiness. A fever in a baby under 3 months also needs prompt care. This information is based on U.S. (AAP and CDC) guidance; if you live elsewhere, check with a local pediatrician. This information isn’t a diagnostic tool and doesn’t replace advice from a medical professional.