What Does Your Phlegm Say About Your Health? The Body's Messages You Might Not Know - "Alternative Indicators" Doctors Observe

Every winter, the question that inevitably arises is, "Do I need antibiotics because my mucus (phlegm) is green?" In drugstore aisles and family LINE chats, anxiety spikes just because the "color" changes. An article published in The Independent (reposted from The Conversation) carefully unravels this "color myth" and points out "what you should really be looking at." The Independent

1) What is mucus for in the first place?

Nasal and airway mucus is not just an "unpleasant thing." It acts as a **"defense filter"** that captures dust, particles, and pathogens in the air to prevent them from entering the body and carries them out. Normally, cilia on the surface of the airways transport mucus, and we are mostly unaware of its presence. However, when infections or inflammations occur, the cilia can be damaged or overwhelmed, causing mucus to accumulate and requiring "expulsion from the body" through coughing or blowing the nose. The Independent

Additionally, similar things can happen with allergies. The immune system overreacts to pollen or dust, increasing mucus and creating a state where it feels like a cold but without a fever. Excessive mucus secretion can also occur in chronic conditions such as asthma, cystic fibrosis, and COPD. The Independent

2) Why does it become "thick"?—The story of moisture and "mucin"

Healthy mucus is composed of **about 90-95% moisture**, with the remainder consisting of mucin (a protein responsible for stickiness) and salts. Therefore, regular nasal mucus is clear and thin. CSIRO

However, during or after fighting an infection, mucin increases, raising viscosity and making the mucus "thicker." As a result, nasal congestion may become more severe, or postnasal drip may cause coughing. The Independent

3) The main topic: What does the "color" of phlegm and mucus mean?

The article realistically organizes the changes in color.

White to cloudy (whitish/cloudy color)

This is often seen in the early stages of infection (commonly known as the beginning of a cold), but can also occur with allergies or asthma-related inflammation. The Independent

Yellow to green to brown

Common in the later stages of infection. This is where misunderstandings arise.
The green or yellow-green color can be attributed to enzymes like myeloperoxidase released by immune cells. While it is a sign that "the body is fighting," it cannot be simply concluded as "green means bacteria.". The Independent

Brown to reddish-brown (blood mixed)

If you blow your nose hard enough to damage the mucous membranes, blood may mix with the mucus, turning it reddish-brown (this may not be a major concern in such cases). However, if **coughing up blood (hemoptysis)** occurs, it could indicate serious causes like severe lung infections or cancer, and the article emphasizes consulting a healthcare professional. The Independent

Black

Black mucus is rare and can be caused by fungal infections or exposure to pollutants like dust or tobacco smoke, so a medical consultation is recommended. The Independent

4) "So, do I need antibiotics?"—The answer is "You can't decide based on color alone"

This is the crux of the matter. While doctors may ask about the color and amount of phlegm during diagnosis, patient self-reports may not always match observations. Furthermore, although color charts may be referenced, yellow-green does not necessarily mean bacteria. Therefore, the article clearly states that "you cannot determine the need for antibiotics based on color alone." The Independent

Harvard Health similarly explains that "it is an 'established knowledge' that you cannot distinguish between viral or bacterial (or whether it's an infection) based solely on the color or viscosity of mucus," and advises against expecting antibiotics just because it's green. Harvard Health

Cleveland Clinic also states that "you cannot determine the specific type of infection based on mucus color 'alone'" and recommends consulting a doctor if there are concerning symptoms. Cleveland Clinic

5) Guidelines for consulting a doctor: "Course and warning signs" over "color"

The article provides practical guidelines as follows.

• Temporary relief may be achieved with hydration or nasal sprays The Independent

• However, if fever, severe fatigue, or loss of appetite persists for more than 1-2 weeks, consult a healthcare professional The Independent

• Blood-streaked phlegm, shortness of breath, chest pain, black phlegm require more attention (consultation recommended) The Independent

Additionally, the UK's public health authority (formerly PHE, now information related to UKHSA on GOV.UK) also clearly refutes the misconception that green phlegm = antibiotics, and lists highly urgent symptoms such as difficulty breathing, chest pain, and blood-streaked phlegm. GOV.UK

6) Reactions on social media: Why does this topic "ignite" every year?

The theme of this article tends to simultaneously elicit responses on social media such as "I get it," "Why didn't you say that sooner," and "But in practice..."

Reaction 1: Anxiety and "self-diagnosis" of the "green = antibiotics" camp

• "I went to the hospital thinking it was bacterial because it turned green."

• "I can't take time off work, so I want medicine (antibiotics) that will make me better quickly."
  This type of background has a pressing desire to "get better quickly." On the other hand, GOV.UK materials also introduce data showing that a certain percentage of the general public believes "antibiotics work for a cough with green phlegm," indicating that the misunderstanding is deeply rooted. GOV.UK

Reaction 2: Healthcare professionals and medical accounts countering with "Don't decide based on color alone"

On social media, many healthcare professionals post strong warnings. For example, medical posts on Instagram repeatedly convey the message that "even if it's green or yellow, that alone doesn't mean antibiotics are necessary." instagram.com

On Facebook, educational posts denying the "myth" that "green mucus = antibiotics" can also be seen. Facebook

Reaction 3: The realists who say, "But there are exceptions, right?"

This is where the discussion becomes complicated. In reality, there are research and clinical contexts where the color of phlegm can be part of clinical judgment, such as in chronic airway diseases (e.g., COPD exacerbations). PMC

On social media, a common conclusion is that "color 'alone' is not enough, but it can be informative when combined with other symptoms."

7) Conclusion: The "story" over "color" is what should be checked

The color of nasal mucus and phlegm serves as "background information" indicating that the immune system is working inside the body. However, color is not the decisive factor for diagnosis.
What should be noted are (1) how long it has lasted, (2) whether there are systemic symptoms, and (3) whether there are warning signs. By focusing on these, unnecessary anxiety and unnecessary antibiotics can be reduced.

In conclusion, the message of this article can be summed up as follows.
"Don't panic even if it's green. However, if 'something different than usual' persists, don't hesitate to consult." The Independent