What Illnesses Cause Drainage? A Comprehensive Guide

September 27, 2025 •

4 min read

Fact: The average adult gets 2–3 colds per year, a prime example of a viral illness that causes drainage. Understanding what illnesses cause drainage is crucial for identifying the root problem and taking appropriate action for your health.

Quick Summary

Drainage is a common symptom of various illnesses, including respiratory infections like colds, the flu, and sinusitis, as well as allergic rhinitis, ear infections, and more serious conditions like pneumonia.

Key Points

Common Culprits: Nasal drainage is most often caused by respiratory infections like colds, the flu, or sinusitis.
Symptom of Allergy: Allergic rhinitis, or hay fever, triggers a runny nose with clear, watery discharge.
Signs of Infection: Thick, yellow, or green mucus can indicate a bacterial infection like sinusitis or pneumonia.
Warning in the Ear: Ear drainage, especially pus-like fluid, can be a sign of a ruptured eardrum from an infection.
Serious Conditions: Less common but more severe causes include pleural effusion (fluid on the lungs) and lymphatic disorders.
Listen to Your Body: The location, color, and consistency of drainage are key indicators of the underlying health issue.

Understanding Drainage: More Than Just a Runny Nose

Drainage, medically known as effluvium or discharge, is the body's natural response to inflammation, infection, or irritation. While often associated with a runny nose (rhinorrhea), drainage can manifest in many forms and from different parts of the body. Its color, consistency, and location can provide valuable clues about the underlying health issue.

The Body's Protective Mechanism

When foreign invaders like viruses, bacteria, or allergens enter the body, the immune system triggers a response. In the sinuses and nasal passages, this involves increasing mucus production to trap and flush out these irritants. In the case of an ear infection, fluid builds up behind the eardrum to fight the bacteria or virus. This is why drainage is a symptom of so many different conditions—it’s the body’s way of self-cleaning and healing.

Common Respiratory Infections Causing Drainage

Colds and the Flu

Viral infections are the most common cause of nasal drainage. During a cold or the flu, the body produces clear, watery mucus that gradually thickens and can change color to white, yellow, or green as the immune system works to fight the infection. This is a normal part of the healing process.
Postnasal drip, where mucus drains down the back of the throat, is a classic symptom of these illnesses and can lead to a sore throat and coughing.

Sinusitis (Sinus Infection)

Sinusitis occurs when the tissue lining the sinuses becomes inflamed and swollen. This blocks the drainage ports, allowing fluid to build up and become infected with bacteria or viruses.
Symptoms include thick, discolored nasal discharge, facial pressure, headaches, and sometimes a reduced sense of smell.
Treatment often involves decongestants, saline sprays, and, in bacterial cases, antibiotics.

Bronchitis and Pneumonia

Bronchitis, an inflammation of the bronchial tubes, often causes a persistent cough that produces clear, white, or yellowish-gray mucus.
Pneumonia can cause a more serious, thicker drainage of phlegm that can be green or even blood-tinged, as fluid and pus build up in the lungs.

Chronic Conditions and Allergies

Allergic Rhinitis (Hay Fever)

Triggered by allergens like pollen, dust mites, or pet dander, this condition causes the immune system to release histamines.
Symptoms include clear, watery nasal drainage, sneezing, and itchy eyes.
Management involves avoiding triggers and using antihistamines or steroid nasal sprays.

Non-Allergic Rhinitis

For some, constant postnasal drainage is not caused by allergies. This non-allergic rhinitis can be triggered by irritants like smoke, perfumes, or strong odors, and can also be affected by temperature changes or hormonal fluctuations.

Less Common but Serious Causes

Ear Infections (Otitis Media)

Common in children, ear infections cause fluid to build up behind the eardrum.
Drainage occurs if the pressure causes the eardrum to tear or rupture, releasing cloudy or pus-like fluid.
Warning signs also include ear pain and muffled hearing.

Pleural Effusion

Also known as "water on the lungs", this condition involves excess fluid accumulating in the space between the lungs and the chest wall.
It can be caused by infections like pneumonia, cancer, or heart failure.
Symptoms include chest pain, shortness of breath, and rapid breathing.

Lymphatic Disorders

Conditions like lymphedema are caused by a problem with the lymphatic system, which normally drains excess fluid from tissues.
Damage to the lymphatic system can cause fluid buildup and drainage, particularly after certain cancer treatments or injuries.

Comparison Table: Drainage Types and Their Potential Causes


Type of Drainage	Description	Common Causes
Clear, Watery	Thin, resembles water	Viral infections (cold, flu), allergies, non-allergic rhinitis
Cloudy or Pus-like	Thick, yellow, green, or brown	Bacterial sinus infection, ear infection with ruptured eardrum, pneumonia
Bloody	Contains blood	Sinus irritation, nose trauma, severe respiratory infections, nasal polyps
Serosanguineous	Thin, pinkish or tinged with blood	Nasal irritation or early stages of some infections
Thick Mucus	Heavy, difficult to clear	Sinusitis, colds progressing, dehydration

When to Seek Medical Help for Drainage

While many cases of drainage resolve on their own, certain signs indicate the need for a doctor's visit. A visit is warranted if you experience drainage along with any of the following:

A high fever that lasts for several days.
Symptoms that worsen or persist for more than a couple of weeks.
Difficulty breathing or shortness of breath.
Facial pain or pressure that is severe.
Blood-tinged or foul-smelling drainage.
Changes in hearing or severe ear pain.
Drainage from a wound that is thick, pus-like, or has a strong odor.

A healthcare professional can perform a proper diagnosis and recommend the correct course of action, which may include antibiotics for bacterial infections or other targeted treatments. For more information on general respiratory health, consult resources from the Centers for Disease Control and Prevention.

Conclusion

Drainage is a broad symptom caused by a variety of illnesses, from the very common to the more serious. Paying attention to its characteristics—such as color, consistency, and accompanying symptoms—can help you better understand what is happening in your body. In many cases, it's a sign of a mild, self-limiting infection, but if symptoms are severe or persist, it's always best to seek medical advice for an accurate diagnosis and treatment plan.

Frequently Asked Questions

Green or yellow drainage is often associated with a bacterial infection, like sinusitis or pneumonia. While a virus can cause a change in mucus color over time, persistent discolored discharge is a strong indicator of a bacterial issue.

Yes, allergies are a very common cause of drainage. When you are exposed to an allergen, your immune system releases histamine, which causes your nasal passages to swell and produce clear, watery mucus.

Postnasal drip is the sensation of mucus draining down the back of your throat. It can feel like a tickle or a constant need to clear your throat, and it often leads to a persistent cough, especially at night when lying down.

Ear drainage can be a symptom of a simple ear infection, but it can also signify a ruptured eardrum or swimmer's ear. While most cases are not serious, it is important to see a doctor for a proper diagnosis, especially if you also experience pain, fever, or hearing changes.

While both can cause drainage, a sinus infection typically presents with thicker, more discolored mucus, along with significant facial pressure, pain around the eyes and forehead, and a prolonged duration of symptoms compared to a common cold.

Yes, chronic acid reflux (GERD) can trigger excess mucus production in the airways, leading to a condition called postnasal drip. The stomach acid irritates the throat, prompting a protective mucus response.

Pneumonia and bronchitis are prime examples of illnesses that cause drainage, or phlegm, from the lungs. This type of drainage is often produced with a cough and can be a sign of a more serious respiratory infection.