Yellow phlegm is typically a sign of a respiratory infection, like bronchitis, strep throat or pneumonia. These can be triggered by bacteria or viruses that invade the respiratory tract.

Yellow phlegm is usually the result of immune cells mixing with clear mucus produced by the lungs. Inflammation caused by an infection, allergies or other disease processes can trigger the immune system to send white blood cells to the area, giving phlegm a more yellow color and a thicker texture. This is one of the body's defense mechanisms to help collect any microorganisms along the tract so that they can be coughed up.

If you notice yellow phlegm and it is accompanied by other symptoms like fever, sore throat, or shortness of breath, you should see your doctor for assessment. Learn more about what different phlegm colors mean and how to treat phlegm.

What causes yellow phlegm?

Yellow phlegm can occur for the following reasons:

1. Strep throat

Bacterial pharyngitis, or strep throat, is characterized by swelling of the pharynx due to a bacterial infection. In addition to yellow phlegm, some people may also experience intense sore throat, difficulty swallowing, fever and headache.

Read more about the symptoms, causes and treatment of strep throat.

How to treat: If you suspect pharyngitis, you should see your doctor for evaluation. Treatment should be initiated, and may involve the use of antibiotics and analgesics to reduce inflammation, relieve pain and reduce any fever. Learn more about sore throat medications that the doctor may prescribe.

2. Sinusitis

The presence of yellow phlegm may be a sign of bacterial sinusitis. This condition is characterized by swelling of the nasal cavities due to a bacterial infection.

With this condition, it is also common to notice a runny nose, fever, headache and difficulty breathing due to a plugged nose.

How to treat: Treatment for bacterial sinusitis should be monitored by a doctor. After evaluating your symptoms and confirming diagnosis, the doctor may prescribe antibiotics and other sinusitis medication. Inhaling warm vapor, or nebulizers, may also help to unplug your nose and facilitate breathing.

Check out other natural remedies for sinusitis you can try at home to relieve your symptoms quickly.

3. Bronchitis

Yellow phlegm may emerge in cases of bacterial bronchitis. This condition is characterized by swollen bronchi that produce a thicker mucus, which helps to eliminate any bacteria through coughing.

Other common symptoms of bronchitis include coughing, shortness of breath, fever and fatigue.

How to treat: If your yellow phlegm may be occurring due to bronchitis, you should see your doctor for assessment and to start treatment. Treatment usually involves the use bronchitis medications like bronchodilators, anti-inflammatories, corticosteroids, and expectorants. Drinking lots of fluid can also help to eliminate mucus.

Learn more about home remedies for bronchitis that can help to relieve symptoms and speed-up recovery.

4. Pneumonia

Bacterial pneumonia is usually not contagious, but it can cause the production of yellow phlegm due to built-up bacteria in the lungs. It This condition may also result in green phlegm.

In addition to yellow phlegm, pneumonia can cause other symptoms like fever, chest pain, difficulty breathing and coughing. Learn about the symptoms of pneumonia and what can cause it.

How to treat: Treatment for pneumonia usually involves the use of antibiotics, which are prescribed by a doctor following a thorough chest assessment. Read more about home remedies for pneumonia that can relieve symptoms like fever and coughing.

5. Pulmonary bronchiectasis

Yellow phlegm may also be associated with pulmonary bronchiestasis. This condition is characterized by increased dilation of the bronchi, due to an obstruction in the respiratory airways or due to a bacterial infection. It increases the production of thicker respiratory secretions.

One of the most common symptoms of bronchiestasis is phlegm, however you may also experience coughing with blood, shortness of breath, general malaise or chest pain.

How to treat: Although there is no cure for this condition, treatment can be recommended to reduce symptoms. It may involve the use of antibiotics and bronchodilators to facilitate breathing.

Learn about the different home remedies you can use to get rid of your phlegm faster.

6. Cystic fibrosis

Cystic fibrosis is a genetic disease that affects a protein in the body, known as CFTR. It is characterized by very thick and viscous secretions that are difficult to eliminate, accumulating mainly in the lungs and digestive tract.

In addition to yellow phlegm, other symptoms can also emerge, such as difficulty breathing,persistent shortness of breath, bulky and greasy stools, and constipation.

How to treat: Treatment for cystic fibrosis usually involves the use of prescription medications, like bronchodilators, antibiotics, mucolytics and pancreatic enzymes.

Some patients may also benefit from respiratory physiotherapy sessions and nutritional monitoring with the aim of controlling the disease and improving quality of life.

7. Smoking

The harmful toxins found in cigarettes can irritates the airway and your lungs, stimulating an inflammatory response along the respiratory tract. This can trigger increased mucus production as well as the release of immune cells, which give mucus a yellow color when coughed up.

Yellow phlegm can be coughed up by smokers at any time of the day, but is most commonly seen in the morning, upon waking.

How to treat: Ideally, smoking cessation is the best way to treat yellow phlegm caused by smoking. You should speak to your doctor about strategies that can help you quit smoking permanently, like nicotine replacement therapy, hypnotherapy and psychotherapy.

If your coughing persists for several weeks and continues to present with yellow or brown phlegm, you should see your doctor for assessment, as this can be a sign of lung disease or even lung cancer.

8. Postnasal drip

Your nose naturally produces mucus on a daily basis to help keep your airways and sinuses hydrated and free from debris. It is also a natural defense mechanism that helps to protect your from foreign invaders, like bacteria, viruses or fungi.

However, an over-production of mucus, from allergies, changes in the weather, certain foods or infections for example, can lead to a stickier thicker mucus. This excess mucus can drip into your throat and mix with your saliva, turning into a phlegm with a yellow or brown color.

How to treat: Identifying the underlying trigger of the postnasal drip will help to reduce the amount of yellow phlegm coughed up. This may involve conservative measures, like avoiding allergens and protecting yourself from harsh weather conditions. However, moderate yellow phlegm from postnasal drip may require more targeted treatment, like antihistamines, antibiotics or nasal sprays.