Phlegm, also known as sputum, is mucus that is coughed up from the lower respiratory tract. Phlegm can appear clear, white, yellow, green, brown, grey, or bloody. The color of phlegm can provide clues as to whether an infection is viral or bacterial.
What is Phlegm?
Phlegm is produced by the mucous membranes that line the respiratory tract. It traps irritants like dust, bacteria, and viruses before they can reach the delicate tissues of the lungs. Phlegm is composed of water, proteins, carbohydrates, and lipids.
Some key facts about phlegm:
- Helps protect the respiratory system from infection
- Produced by goblet cells in the mucous membranes
- Contains mucins, immunoglobulins, lipids, proteins
- Can be clear, white, yellow, green, grey, brown, or bloody
Phlegm is usually swallowed unconsciously or coughed up. Increased phlegm production is the body’s way of trying to remove irritants and infectious agents from the respiratory tract.
What Causes Yellow Phlegm?
Yellow phlegm is typically a sign of an underlying respiratory infection. It occurs when white blood cells called neutrophils rush to the site of infection. These specialized white blood cells produce an enzyme called myeloperoxidase that is yellow. When there is a high concentration of neutrophils, the phlegm takes on a yellow or greenish color.
Some common causes of yellow phlegm include:
- Viral respiratory infections like the common cold or flu
- Bacterial infections like bronchitis or pneumonia
- Inflamed airways from asthma or allergies
- Smoking cigarettes or exposure to pollutants
In most cases, yellow phlegm resolves once the infection clears. However, if it persists for more than 10 days or worsens over time, it’s best to see a doctor to determine the underlying cause.
Yellow Phlegm with Viral Infections
Yellow phlegm often indicates the body is fighting off a viral infection like a cold, flu, bronchitis, or pneumonia. Here’s a breakdown of viral infections that can cause yellow phlegm:
Common Cold
The common cold is caused by rhinoviruses, adenoviruses, coronaviruses, and other viruses. Cold symptoms usually come on gradually and include:
- Runny or stuffy nose
- Sore throat
- Coughing
- Sneezing
- Mild body aches
- Mild headache
- Low fever
Yellow phlegm may appear as the cold runs its course, typically lasting 7-10 days. The yellow color signifies the immune system is fighting off the virus.
Influenza
Influenza (the flu) is caused by influenza viruses A and B. Flu symptoms often come on suddenly and include:
- Fever and chills
- Body and muscle aches
- Fatigue
- Cough
- Sore throat
- Runny or stuffy nose
- Headaches
- Vomiting and diarrhea (more common in children)
With influenza, yellow phlegm may appear as the immune system responds to the virus. The flu usually lasts 1-2 weeks.
Viral Bronchitis
Viral bronchitis occurs when viruses infect the bronchi or airways. Symptoms include:
- Dry, hacking cough
- Low fever
- Chest discomfort
- Sore throat
- Headache
- Fatigue
- Runny nose
Yellow mucus often appears as the virus runs its course, usually 7-10 days. The yellow color signals the immune system is battling the virus.
Viral Pneumonia
Viral pneumonia is inflammation of the lungs caused by viruses. Symptoms tend to develop over a few days and may include:
- Dry cough
- Fever
- Chills
- Shortness of breath
- Fatigue
- Muscle aches
Yellow or green phlegm can develop as the immune system responds to the viral infection in the lungs. Viral pneumonia usually improves on its own within 1-3 weeks.
Yellow Phlegm with Bacterial Infections
While yellow phlegm can be present with a viral infection, it may also indicate a bacterial infection such as:
Bacterial Bronchitis
Bacterial bronchitis occurs when bacteria infect the bronchi. Symptoms include:
- Cough with yellow/green phlegm
- Shortness of breath
- Chest discomfort
- Low fever
- Chills
- Sore throat
- Fatigue
Yellow or green phlegm indicates the immune system is fighting a bacterial infection. Bacterial bronchitis usually improves with antibiotics within 7-10 days.
Bacterial Pneumonia
Bacterial pneumonia is an infection of the lungs caused by bacteria like Streptococcus pneumoniae. Symptoms tend to come on more suddenly and severely compared to viral pneumonia. They include:
- High fever
- Cough with yellow/green phlegm
- Chills
- Shortness of breath
- Rapid, shallow breathing
- Chest pain when breathing deeply or coughing
The yellow or green color signals bacteria are present in the lungs. Bacterial pneumonia is treated with antibiotics and usually improves within 1-3 weeks.
Other Causes of Yellow Phlegm
Some other causes of yellow phlegm may include:
- Allergies – Allergic rhinitis can cause yellowish nasal mucus.
- Environmental irritants – Cigarette smoke, air pollution, and chemical fumes can all cause yellow phlegm.
- Gastroesophageal reflux disease (GERD) – Stomach acid backing up into the esophagus can irritate the throat and lungs, leading to increased yellow mucus.
- Cystic fibrosis – This genetic disorder causes excess mucus production, which is often yellow.
So in summary, while yellow phlegm can occur with viral infections like a cold or flu, it more commonly indicates the presence of bacteria, such as in bacterial bronchitis or pneumonia. The yellow color results from an influx of neutrophils rushing to the site of infection.
See a doctor if yellow phlegm persists for more than 10 days or is accompanied by worsening symptoms. Proper diagnosis and treatment can help clear up the infection.
How to Get Rid of Yellow Phlegm
Here are some tips for getting rid of yellow phlegm:
- Get plenty of rest – This allows the immune system to focus energy on fighting infection.
- Stay hydrated – Drink lots of water to thin out mucus.
- Use a humidifier – Moisture in the air helps loosen and clear excess phlegm.
- Take expectorants – Over-the-counter cough medicines like guaifenesin can help thin mucus.
- Use nasal saline spray – Saline helps thin nasal secretions and clear irritants.
- Try steam inhalation – Inhaling warm, moist air helps open airways and loosen phlegm.
- Use cough drops – Cough drops with menthol or eucalyptus help soothe sore throat and thin mucus.
- Avoid irritants – Don’t smoke or expose yourself to pollutants and allergens.
See a doctor if phlegm doesn’t clear with home treatment or if symptoms worsen. Antibiotics may be needed for bacterial infections. With proper treatment, yellow phlegm should resolve once the underlying cause is addressed.
When to See a Doctor
Consult a doctor if you experience any of the following:
- Yellow phlegm persists more than 10 days
- Shortness of breath or difficulty breathing
- High fever above 102°F
- Blood in phlegm
- Face pain from sinus pressure
- Worsening cough or chest congestion
- Severe fatigue or weakness
Seeking timely medical care allows proper diagnosis and treatment to help you recover more quickly.
The Bottom Line
To summarize, yellow phlegm is a sign of an active immune response in the respiratory tract. While it can occur with viral infections, it more commonly indicates a bacterial infection is present. Yellow phlegm results from large numbers of neutrophils rushing to the site of infection.
See a doctor if symptoms like high fever, shortness of breath, or bloody phlegm develop. With appropriate diagnosis and treatment, yellow phlegm should clear once the infection runs its course. Drink plenty of fluids, use cough medication, and get enough rest to help your body recover more quickly.