Adventitious breath sounds are abnormal sounds heard through a stethoscope during breathing. They layer on top of the normal, soft whooshing sound your lungs make and signal that something is interfering with airflow or lung function. The main types are crackles, wheezes, rhonchi, stridor, and pleural friction rubs, each pointing to different problems in different parts of the respiratory system.
How These Sounds Are Detected
A healthcare provider listens to your lungs using a stethoscope in a process called auscultation. You’ll be asked to sit upright and breathe deeply through your mouth. The stethoscope is placed at the top of your chest and moved downward, comparing the left and right sides at each point. Then the same process is repeated on your back. One full breath cycle is assessed at each location. This side-to-side comparison is key: if one lung sounds different from the other, or if extra sounds appear in specific areas, that narrows down what’s going on.
The timing of an abnormal sound within the breath cycle matters just as much as the sound itself. A noise heard only when you breathe in suggests different problems than one heard when you breathe out, and some sounds occur during both phases.
Crackles: Brief Popping or Clicking
Crackles are short, sharp, non-musical sounds, sometimes compared to the noise of pulling apart Velcro or crumpling cellophane. They come in two forms: fine and coarse.
Fine crackles are high-pitched, quiet, and very brief. They happen when small airways that have collapsed shut suddenly pop open during inhalation. These are commonly associated with conditions that cause fluid or scarring in the lung tissue, such as pneumonia, pulmonary fibrosis, or heart failure that has backed fluid into the lungs.
Coarse crackles are lower-pitched, louder, and last a bit longer. They’re typically related to mucus or other secretions sitting in the larger airways. You might hear them in conditions like bronchitis or in people who have difficulty clearing mucus from their lungs. Because they’re caused by secretions, coarse crackles can sometimes change or shift after coughing.
Wheezes: A Musical, High-Pitched Tone
A wheeze is a continuous, musical sound lasting longer than 250 milliseconds. It’s produced when airway walls narrow almost to the point of touching, and the remaining airflow causes them to vibrate against each other. Most wheezes are heard during exhalation, though they can occur during inhalation as well.
Wheezing is the hallmark sound of narrowed lower airways. Asthma and COPD are the most common causes, but wheezing can also result from allergic reactions, respiratory infections, or anything that causes swelling or constriction inside the bronchial tubes. A single-note wheeze tends to suggest narrowing in one airway, while multiple notes heard across the chest point to widespread narrowing.
Squawks
A squawk is essentially a very short wheeze, almost entirely heard during inhalation. It occurs when a closed airway snaps open and its walls briefly vibrate against each other before separating. Squawks are less common and are sometimes heard in conditions affecting the smaller airways or lung tissue.
Rhonchi: Low-Pitched Snoring Sounds
Rhonchi are continuous, low-pitched sounds often described as snoring or gurgling. They’re best heard when you breathe out and are caused by mucus or fluid vibrating in the larger airways. One distinguishing feature of rhonchi is that coughing can move the sound around to different parts of the chest as it shifts the mucus responsible for it.
Rhonchi show up in conditions that increase mucus production or reduce your ability to clear secretions, such as chronic bronchitis, COPD flare-ups, or pneumonia. Because they’re tied to mucus rather than structural changes, rhonchi are sometimes the most “fixable” of the adventitious sounds: suctioning, coughing, or mucus-thinning treatments can reduce or eliminate them.
Stridor: A Warning From the Upper Airway
Stridor is a high-pitched, harsh sound heard over the throat and upper windpipe. Unlike wheezes, which originate in the lower airways inside the lungs, stridor is generated by turbulent airflow through a partially blocked upper airway. It typically becomes audible when the upper airway narrows to about 5 millimeters or less.
The timing of stridor helps locate the problem. Inspiratory stridor (heard when breathing in) suggests the obstruction is at the level of the voice box. Expiratory stridor points to a blockage lower down, in the windpipe or large bronchi. Biphasic stridor, heard during both inhalation and exhalation, suggests the narrowing is right at or just below the vocal cords.
Stridor is generally treated with more urgency than other adventitious sounds because it signals that the main airway is compromised. In children, a swollen epiglottis (the flap that covers the windpipe during swallowing) is a particularly dangerous cause. In adults, stridor can result from severe allergic reactions, tumors, foreign bodies, or swelling after a medical procedure. It should not be confused with stertor, which is a lower-pitched snoring sound that originates in the nose or back of the throat.
Pleural Friction Rub: Creaking Leather
A pleural friction rub sounds like creaking old leather or the squeak of two rough surfaces rubbing together. It happens when the two thin membranes surrounding the lungs, called the pleura, become inflamed, coated with sticky deposits, or thickened. Normally, a thin layer of fluid keeps these membranes sliding silently past each other during breathing. When that smooth glide is disrupted, the friction produces an audible rub.
Pleural rubs are heard during both inhalation and exhalation and tend to be localized to one area of the chest. Pleurisy (inflammation of the pleural lining) is the most common cause, often from infection, but it can also occur with blood clots in the lung or, less commonly, cancer invading the pleural surface. One useful clinical test: if the sound stops when you hold your breath, it’s coming from the pleura. A similar-sounding rub from the membrane around the heart (the pericardium) will continue because the heart keeps beating regardless.
What the Sound Pattern Tells You
No single adventitious sound is a diagnosis on its own. Providers interpret these sounds in combination with where they’re heard, when in the breath cycle they appear, and whether they change with coughing or position changes. Crackles at the base of both lungs that worsen when lying flat, for instance, paint a very different picture than a wheeze heard across the entire chest during a cold.
The international respiratory community, through a task force led by the European Respiratory Society, has worked to standardize the names and definitions of these sounds. The agreed-upon categories are crackles (fine and coarse), wheezes (high-pitched continuous sounds), rhonchi (low-pitched continuous sounds), squawks, stridor, and pleural friction rubs. Older terms like “rales” for crackles still appear in some medical notes but are gradually being replaced.
If a provider hears adventitious breath sounds during your exam, the next steps depend entirely on the type of sound, its location, and your other symptoms. Imaging like a chest X-ray, breathing tests, or in some cases direct visualization of the airway with a small camera may follow. The sounds themselves are a starting point, guiding the provider toward the right part of the respiratory system to investigate further.