Abnormal Lung Sounds: Types, Causes, and Warning Signs

Lung sounds are the noises made as air moves in and out of the respiratory system. Most of the time, breathing is quiet and easy to ignore. But when the airways become narrowed, blocked, irritated, or filled with mucus or fluid, breathing can sound different.

Some lung sounds are harmless and temporary, while others may point to a medical problem that needs attention.

Learning the basic types of lung sounds can help you better understand your symptoms, communicate with your healthcare provider, and recognize when breathing changes should not be ignored.

What Are Lung Sounds?

Lung sounds, also called breath sounds, are the sounds produced when air moves through the lungs and airways. A healthcare provider usually listens to these sounds with a stethoscope placed on the chest, back, or sides. This exam is called auscultation.

Normal lung sounds are usually soft, smooth, and steady. They are created as air flows through the windpipe, bronchial tubes, and smaller airways inside the lungs. In a healthy person, these sounds are usually quiet and even on both sides of the chest.

Abnormal lung sounds happen when something interferes with normal airflow. Swelling, mucus, fluid, airway narrowing, infection, inflammation, or reduced lung expansion can all change the way breathing sounds. Common abnormal lung sounds include wheezing, crackles, rhonchi, stridor, diminished breath sounds, and pleural friction rubs. These are sometimes called adventitious breath sounds, which simply means extra or abnormal sounds heard during breathing.

It is important to understand that lung sounds are clues, not a diagnosis. A provider does not rely on sound alone to determine what is wrong. They also consider symptoms, medical history, oxygen levels, temperature, breathing rate, heart rate, and sometimes imaging or lab tests.

Why Lung Sounds Matter

Lung sounds matter because they can reveal changes in airflow and lung function. For example, a high-pitched whistling sound may suggest narrowed airways. A bubbling or crackling sound may suggest fluid, infection, or stiff lung tissue. A rattling sound may point to mucus in the larger airways. Very quiet breath sounds may suggest that air is not moving well in part of the lungs.

For the general public, understanding lung sounds can be useful because it helps you describe what you are experiencing. Instead of only saying, “My breathing sounds strange,” you may be able to explain that you hear a whistle when you breathe out, a rattling sound when you cough, or a harsh noise when you breathe in. These details can help your healthcare provider decide what to ask, what to examine, and what tests may be needed.

However, lung sounds should always be interpreted in context. A temporary rattle during a cold may be caused by mucus that clears with coughing. Persistent wheezing with shortness of breath may suggest asthma, COPD, an allergic reaction, or another condition. Crackles with fever may raise concern for pneumonia, while crackles with swelling in the legs may point toward fluid buildup related to heart problems. The same sound can have different meanings depending on the situation.

Normal Breath Sounds

Normal breath sounds are usually described as clear, soft, and smooth. When a provider listens to the chest, they expect to hear air moving evenly through both lungs. The sounds may be louder over the upper chest and slightly softer toward the lower lungs, but they should generally be similar from side to side.

Normal breathing should not sound harsh, musical, bubbling, rattling, or squeaky. It should also not be associated with major effort. If someone is breathing normally, they should usually be able to speak in full sentences, maintain normal color, and breathe without obvious distress.

That said, normal breathing can vary. Breath sounds may be quieter in people who take shallow breaths, have a larger body size, or are not breathing deeply during an exam. They may also sound different depending on the position of the body. This is why providers usually listen to several areas of the chest and back rather than relying on one spot.

Wheezing

Wheezing is one of the most common abnormal lung sounds. It is usually described as a high-pitched whistling or musical sound. It is often easier to hear when a person breathes out, although it can sometimes happen during inhalation as well.

Wheezing usually occurs when the airways become narrowed. When air is forced through a tighter space, it can create a whistling sound. This narrowing may happen because of airway swelling, mucus, inflammation, muscle tightening around the airways, or irritation from smoke, allergens, or infection.

Asthma is one of the most common causes of wheezing. During an asthma flare-up, the airways become inflamed and sensitive. The muscles around the airways may tighten, and extra mucus may develop. Together, these changes make it harder for air to move out of the lungs, which can produce wheezing.

COPD can also cause wheezing. COPD is a long-term lung disease that includes chronic bronchitis and emphysema. People with COPD may have narrowed airways, mucus production, and reduced airflow, especially during flare-ups. Respiratory infections, such as bronchitis or pneumonia, can also cause wheezing, particularly when the airways are irritated or swollen.

Allergic reactions are another possible cause. Mild allergies may cause coughing or chest tightness, while severe allergic reactions can cause airway swelling and serious breathing trouble. Wheezing that appears suddenly after exposure to a food, medication, insect sting, or other allergen should be taken seriously, especially if it occurs with swelling, hives, dizziness, or trouble breathing.

Wheezing does not always mean a person has asthma, and not all asthma attacks produce loud wheezing. In severe cases, airflow may become so limited that wheezing becomes very faint or disappears, even though the person is in serious distress. This is one reason symptoms and overall appearance matter as much as the sound itself.

Crackles

Crackles are short, popping, clicking, or bubbling sounds heard during breathing. They are often heard when a person breathes in. Some people compare crackles to the sound of bubble wrap, Rice Krispies cereal, or hair being rubbed between the fingers near the ear.

Crackles can happen when small airways or air sacs open suddenly during inhalation. They can also occur when air moves through fluid or secretions in the lungs. Providers may describe crackles as fine or coarse. Fine crackles tend to be softer, shorter, and higher pitched. Coarse crackles tend to be louder, wetter, and more bubbling.

Pneumonia is a common cause of crackles. When part of the lung becomes infected, inflammation and fluid can collect in the air spaces. This may produce crackling sounds, especially in the area of infection. Pneumonia may also cause fever, chills, cough, mucus, chest discomfort, fatigue, and shortness of breath.

Heart failure can also cause crackles. In heart failure, the heart may not pump blood as effectively as it should. Fluid can back up into the lungs, making breathing more difficult. Crackles related to fluid buildup are often heard in the lower parts of the lungs and may occur with swelling in the legs, trouble lying flat, waking up short of breath, or sudden weight gain.

Pulmonary fibrosis and other forms of lung scarring may also produce crackles. In these conditions, the lung tissue becomes stiff, making it harder for the lungs to expand normally. The crackles may sound dry or velcro-like. These symptoms are often more gradual and may be associated with worsening shortness of breath over time.

Not all crackles mean something dangerous. Sometimes mild crackles can occur after lying down for a long time and may clear after several deep breaths. But persistent crackles, especially when combined with fever, low oxygen levels, chest pain, or worsening shortness of breath, should be evaluated.

Rhonchi

Rhonchi are low-pitched, coarse sounds that may resemble snoring, rattling, or gurgling. They are often associated with mucus or secretions in the larger airways. Unlike wheezing, which tends to be high-pitched and musical, rhonchi are usually deeper and rougher.

One helpful clue is that rhonchi may change after coughing. If mucus is sitting in a larger airway, coughing may move it, temporarily reducing or changing the sound. This does not always happen, but when it does, it can help suggest that secretions are playing a role.

Bronchitis is a common cause of rhonchi. Bronchitis occurs when the bronchial tubes become inflamed, often due to a viral infection or irritation. People with bronchitis may have a cough, mucus production, chest congestion, fatigue, and a rattling sensation in the chest.

COPD can also cause rhonchi, especially when chronic bronchitis is present. People with chronic bronchitis often produce excess mucus, which can collect in the airways and create rattling sounds. Pneumonia, respiratory infections, and conditions that make it hard to clear secretions can also cause rhonchi.

Rhonchi should be taken more seriously if they are persistent, worsening, or associated with shortness of breath, fever, chest pain, confusion, or low oxygen levels. A person who has a long-term lung disease and develops new or worsening rattling sounds may be experiencing a flare-up or infection.

Stridor

Stridor is a high-pitched, harsh sound that usually happens when breathing in. It often comes from the upper airway, such as the throat, voice box, or upper windpipe. Stridor is different from wheezing because wheezing usually comes from narrowed airways inside the chest, while stridor often suggests narrowing or blockage higher up.

Stridor can be a warning sign because the upper airway is the main pathway for air entering the lungs. If that area becomes swollen, blocked, or narrowed, breathing can become difficult quickly.

In children, stridor may occur with croup, a common viral illness that causes swelling around the voice box and often produces a barking cough. Stridor can also happen if a child inhales a small object, such as food, a toy part, or another foreign body.

In adults, stridor may occur with severe allergic reactions, swelling of the throat, trauma, infection, vocal cord problems, or a mass pressing on the airway. It may also happen after certain procedures involving the airway.

Stridor should not be ignored. Emergency care is needed if stridor occurs with trouble breathing, drooling, swelling of the lips or throat, blue or gray skin, severe anxiety, confusion, or inability to speak normally. Because stridor can signal a serious airway problem, it is one of the lung-related sounds that deserves immediate attention when symptoms are severe.

Diminished Breath Sounds

Diminished breath sounds mean that breathing sounds are quieter than expected. This does not necessarily mean the lungs are silent. It means the provider hears less air movement in a certain area or throughout the chest.

Diminished breath sounds can happen when air is not moving well through the lungs. This may occur during a severe asthma attack or COPD flare-up, when airflow is very limited. In these cases, quiet breath sounds can actually be concerning because they may mean not enough air is getting in or out.

A collapsed lung, also called pneumothorax, can cause diminished or absent breath sounds on one side. This happens when air leaks into the space around the lung, preventing part or all of the lung from expanding normally. Symptoms may include sudden sharp chest pain and shortness of breath.

Fluid around the lung, called pleural effusion, can also reduce breath sounds in a certain area. This fluid sits outside the lung but inside the chest cavity, making it harder for sound to travel normally. Pleural effusion can occur with heart failure, infection, cancer, liver disease, kidney disease, or other medical problems.

Diminished breath sounds may also occur for less serious reasons, such as shallow breathing, obesity, pain with deep breaths, or poor effort during an exam. Still, when breath sounds are reduced along with significant symptoms, the cause needs to be investigated.

Pleural Friction Rub

A pleural friction rub is a grating, scratching, or creaking sound that can happen when the lining around the lungs becomes inflamed. The lungs are covered by a thin lining called the pleura, and the inside of the chest wall has a similar lining. Normally, these layers slide smoothly against each other when you breathe. When they become inflamed, they can rub together and create a rough sound.

A pleural friction rub may be associated with sharp chest pain that gets worse when taking a deep breath, coughing, or moving. This type of pain is sometimes called pleuritic chest pain.

Possible causes include pneumonia, pleurisy, pulmonary embolism, autoimmune disease, chest injury, or other conditions that irritate the pleura. A pleural rub is less common than wheezing or crackles, but it can provide an important clue during a chest exam.

Because some causes of pleuritic chest pain can be serious, sharp chest pain with shortness of breath, coughing blood, fainting, or sudden worsening symptoms should be treated as urgent.

What Causes Abnormal Lung Sounds?

Abnormal lung sounds can have many causes. The sound itself provides clues, but the full picture matters. A person’s age, symptoms, medical history, smoking history, allergies, recent infections, medications, and exposure to irritants can all help narrow down the possibilities.

Common causes of abnormal lung sounds include:

• Asthma
• COPD
• Bronchitis
• Pneumonia
• Respiratory infections
• Allergic reactions
• Mucus buildup
• Heart failure
• Fluid around the lungs
• Collapsed lung
• Lung scarring
• Airway obstruction
• Smoke or chemical irritation
• Foreign object in the airway
• Inflammation of the lung lining

Note: Many of these conditions can overlap. For example, someone with COPD may develop pneumonia, causing both wheezing and crackles. A person with asthma may also have mucus buildup, causing wheezing and rhonchi. Someone with heart failure may have crackles from fluid in the lungs and shortness of breath that worsens when lying flat.

Lung Sounds and Common Conditions

Asthma

Asthma is a long-term condition that causes the airways to become inflamed and sensitive. During an asthma flare-up, the airways may tighten, swell, and produce extra mucus. This can lead to wheezing, coughing, chest tightness, and shortness of breath.

Wheezing is common in asthma, but it is not always present. Some people mainly have coughing, especially at night or after exercise. Others may feel chest tightness without much audible noise. Severe asthma symptoms require prompt medical attention, especially if rescue medication is not helping or breathing becomes difficult.

COPD

COPD is a chronic lung disease that makes it harder to move air in and out of the lungs. It is often linked to smoking, although other exposures can contribute. COPD includes chronic bronchitis and emphysema.

People with COPD may have wheezing, rhonchi, diminished breath sounds, chronic cough, mucus production, and shortness of breath. During flare-ups, symptoms may worsen quickly. A change in mucus color, increased mucus, fever, worsening cough, or greater shortness of breath may suggest infection or an exacerbation.

Pneumonia

Pneumonia is an infection of the lung tissue. It can cause inflammation and fluid buildup in the air spaces. Lung sounds may include crackles, diminished breath sounds in one area, or sometimes rhonchi if mucus is present.

Symptoms may include fever, chills, cough, mucus, chest pain, fatigue, and shortness of breath. Some older adults may have less obvious symptoms, such as confusion, weakness, or reduced appetite. Pneumonia can range from mild to life-threatening, so worsening symptoms should be evaluated.

Bronchitis

Bronchitis occurs when the bronchial tubes become inflamed. Acute bronchitis is often caused by a virus and may develop after a cold. It can cause cough, mucus, chest congestion, wheezing, or rhonchi.

Most cases of acute bronchitis improve with time, but a cough may last for several weeks. Medical care is important if symptoms are severe, if fever persists, if breathing becomes difficult, or if the person has a higher-risk condition such as COPD, asthma, heart disease, or a weakened immune system.

Heart Failure

Heart failure does not mean the heart has stopped. It means the heart is not pumping as well as the body needs. When fluid backs up into the lungs, it can cause shortness of breath and crackles.

People with heart failure may notice trouble breathing when lying flat, waking up gasping for air, swelling in the ankles or legs, fatigue, or sudden weight gain from fluid retention. Crackles with these symptoms should be checked promptly.

Allergic Reactions

Allergic reactions can affect the airways and cause wheezing, coughing, or throat tightness. Mild allergies may cause sneezing, congestion, or mild breathing symptoms. Severe allergic reactions, known as anaphylaxis, can be life-threatening.

Warning signs include wheezing, throat swelling, trouble breathing, hives, dizziness, vomiting, or feeling faint after exposure to a trigger. Sudden wheezing with signs of a severe allergic reaction requires emergency care.

When Lung Sounds Are an Emergency

Some breathing symptoms should be treated as urgent, regardless of the exact sound. Abnormal lung sounds are more concerning when they occur with signs that the body is not getting enough oxygen or that the airway may be blocked.

Seek emergency medical care if abnormal breathing sounds occur with:

• Severe shortness of breath
• Chest pain or pressure
• Blue, gray, or pale lips or fingertips
• Confusion, fainting, or extreme drowsiness
• Trouble speaking in full sentences
• Stridor or noisy breathing at rest
• Swelling of the face, lips, tongue, or throat
• Coughing up blood
• Sudden sharp chest pain with shortness of breath
• Severe wheezing that is not improving
• Signs of a serious allergic reaction

Note: The American Lung Association lists warning signs of lung disease that include chronic cough, shortness of breath, chronic mucus production, wheezing, coughing up blood, and chronic chest pain. These symptoms do not always mean a serious disease is present, but they should not be ignored when persistent or worsening.

When to Make a Doctor’s Appointment

Not every abnormal lung sound is an emergency. Still, some symptoms should be evaluated by a healthcare provider, especially if they do not improve.

Consider making an appointment if you have:

• A cough lasting more than a few weeks
• Recurrent wheezing
• Ongoing chest congestion
• Shortness of breath with normal activities
• Mucus that keeps returning
• Fever with cough or chest symptoms
• Breathing symptoms that wake you up at night
• A known lung condition with new or worsening symptoms
• Frequent respiratory infections
• Unexplained fatigue with breathing changes

Note: A healthcare provider may listen to your lungs, check your oxygen level, ask about your symptoms, and recommend tests if needed. These may include a chest X-ray, blood tests, breathing tests, sputum testing, or other studies depending on the suspected cause.

Can You Hear Abnormal Lung Sounds Without a Stethoscope?

Sometimes, yes. Wheezing, stridor, and loud rattling can sometimes be heard without a stethoscope. A person may hear a whistle when breathing out, a squeak when breathing in, or a rattling sound in the chest.

However, many lung sounds are subtle. Crackles, mild wheezing, and reduced breath sounds may only be detected during a proper exam. This means you should not rely only on what you can hear at home. If you feel short of breath, have chest pain, develop a fever, or notice worsening symptoms, it is worth getting checked even if your breathing does not sound unusual.

The opposite is also true. A sound that seems alarming may sometimes be caused by mucus in the throat or upper airway rather than a serious lung problem. A healthcare provider can help determine where the sound is coming from and whether it needs treatment.

How Healthcare Providers Evaluate Lung Sounds

When a provider listens to your lungs, they usually ask you to breathe in and out through your mouth. They move the stethoscope to different areas of the chest and back to compare both sides. They listen for the loudness, pitch, timing, location, and quality of each sound.

They may pay attention to whether the sound happens during inhalation, exhalation, or both. Wheezing is often more noticeable during exhalation. Crackles are often heard during inhalation. Stridor is often louder during inhalation and may be heard near the neck.

They may also ask you to cough and then listen again. If a rattling sound changes after coughing, mucus may be involved. If a sound remains in the same location, it may suggest a more fixed problem in that part of the lung.

The exam may also include checking oxygen saturation with a pulse oximeter, measuring temperature, counting the breathing rate, and looking for signs of increased work of breathing. These signs may include using neck muscles to breathe, flaring nostrils, pulling in of the skin between the ribs, or difficulty speaking.

What You Can Do at Home

If you have mild symptoms from a cold or temporary chest congestion, simple self-care may help. Staying hydrated can help keep mucus thinner. Rest allows the body to recover. Avoiding smoke, vaping, strong fumes, and other irritants can reduce airway irritation. A humidifier may help some people feel more comfortable, especially when the air is dry.

Coughing can help clear mucus, but persistent or severe coughing should not be ignored. Over-the-counter medications may help some symptoms, but they are not right for everyone. People with chronic health conditions, older adults, pregnant individuals, and those taking multiple medications should ask a healthcare provider or pharmacist before using new medications.

If you have asthma, COPD, or another diagnosed lung condition, follow your prescribed action plan. Use inhalers and medications exactly as directed. Do not wait too long to seek care if symptoms are worsening or your usual treatment is not helping.

Common Myths About Lung Sounds

One common myth is that wheezing always means asthma. Asthma is a common cause, but wheezing can also occur with COPD, infections, allergies, heart-related problems, or airway irritation.

Another myth is that crackles always mean pneumonia. Pneumonia can cause crackles, but so can heart failure, lung scarring, atelectasis, and other conditions. The cause depends on the full set of symptoms and exam findings.

A third myth is that loud breathing is always more serious than quiet breathing. Sometimes loud wheezing can happen with moderate airway narrowing, while very quiet breath sounds can occur when airflow is severely limited. Quiet lungs in a person who is struggling to breathe can be a serious warning sign.

Another misunderstanding is that clear lung sounds always mean nothing is wrong. Some conditions may not produce obvious abnormal sounds early on. A person can still have shortness of breath, low oxygen, blood clots, heart problems, or other issues even if lung sounds are not dramatic.

How to Describe Lung Sounds to Your Doctor

If you notice unusual breathing sounds, try to describe them clearly. You do not need medical terms. Simple descriptions are often helpful.

You can explain whether the sound is:

• Whistling
• Rattling
• Bubbling
• Clicking
• Squeaking
• Snoring
• Harsh
• Wet
• Dry
• Louder when breathing in
• Louder when breathing out
• Improved after coughing
• Worse when lying down
• Worse with exercise
• Associated with chest pain, fever, or mucus

Note: Also mention when it started, whether it is getting better or worse, and whether you have other symptoms. If you have asthma, COPD, heart disease, allergies, or recent illness, share that information too.

Final Thoughts

Lung sounds can provide important clues about what is happening in the airways and lungs. Wheezing may suggest narrowed airways, crackles may point to fluid or inflammation, rhonchi often involve mucus, stridor can signal upper airway narrowing, and diminished breath sounds may mean reduced airflow or poor lung expansion.

Still, lung sounds are only one part of the picture. Symptoms, medical history, oxygen levels, and proper evaluation all matter. If abnormal breathing sounds are new, persistent, worsening, or linked with shortness of breath, chest pain, fever, blue lips, confusion, or coughing up blood, seek medical care promptly.