Pain under the armpit that increases when you breathe is a symptom that can originate from many different structures in the chest wall and surrounding areas. This discomfort is often a response to the mechanical action of the rib cage and diaphragm expanding the chest cavity. The causes range significantly, from simple muscle strains and nerve irritation to more serious conditions involving the lungs or the circulatory system. Because the armpit region is a complex intersection of muscles, nerves, blood vessels, and lymph nodes, pinpointing the source requires careful medical evaluation.
Musculoskeletal and Nerve Sources of Pain
Pain that worsens with deep inhalation is frequently traced back to strained muscles and cartilage of the chest wall. The intercostal muscles, which run between the ribs, help the rib cage expand and contract. These muscles can be strained by sudden movements, heavy lifting, or prolonged coughing episodes. When strained, the act of taking a deep breath stretches the injured muscle, producing sharp, localized pain.
Costochondritis involves inflammation of the cartilage connecting the ribs to the breastbone, or sternum. Although the pain often occurs centrally, it can radiate outward along the ribs toward the armpit area. This condition causes tenderness when pressed and is aggravated by chest wall movement like deep breathing, sneezing, or coughing.
Nerve-related issues can also mimic this pain, such as intercostal neuralgia, which is irritation or compression of the nerves following the path of the ribs. This nerve pain can feel sharp, burning, or aching, and it increases dramatically with activities that expand the rib cage, including a full breath. Intercostobrachial neuralgia specifically involves nerves in the armpit region, causing localized, shooting pain highly sensitive to movement.
Conditions Affecting the Lungs and Chest Lining
Pleuritic chest pain results from irritation of the pleura, the two thin layers of tissue lining the lungs and the inside of the chest cavity. When these layers become inflamed, a condition known as pleurisy, they rub against each other. The defining characteristic is a sharp, stabbing pain that intensifies dramatically with inhalation, exhalation, or a cough.
Pleurisy is often a complication of underlying respiratory infections, such as viral illnesses, bacterial pneumonia, or bronchitis. The infection causes inflammation that extends to the pleural lining, sometimes accompanied by systemic symptoms like fever and a persistent cough.
Pneumothorax, or a collapsed lung, is a severe condition where air enters the pleural space, causing sudden, intense, sharp pain and shortness of breath. The mechanical irritation of the pleura causes pain that is immediately exacerbated by any attempt to breathe deeply.
A pulmonary embolism (PE), a blockage in the lung’s arteries, must be considered as a cause of pleuritic pain. This life-threatening condition often presents with sudden, severe, sharp chest pain, shortness of breath, and a rapid heart rate. The pain arises because the blocked blood flow causes irritation near the pleural surface. Unlike musculoskeletal pain, the pain is generally not reproducible by pressing on the outer chest wall and is often accompanied by systemic symptoms.
Localized Skin and Lymphatic Causes
The armpit is home to a cluster of lymph nodes, which function as filters for the immune system. When these nodes swell in response to infection, injury, or systemic illness, they become enlarged and tender, a condition called lymphadenopathy. The swollen nodes occupy more space, and surrounding tissues become inflamed.
Deep breathing or large arm movements cause the skin and underlying tissues of the axilla to stretch, putting pressure on the swollen lymph nodes. This mechanical stretching makes the pain noticeably worse with respiration, even though the primary problem is not in the lung or muscle tissue.
Dermatological issues specific to the armpit can also cause pain aggravated by breathing. Conditions like a bacterial abscess, folliculitis (hair follicle infection), or the viral infection Herpes Zoster (Shingles) cause intense, localized inflammation and hypersensitivity.
With Shingles, the virus reactivates along a nerve pathway, creating a painful, burning sensation that precedes the characteristic rash. If this pathway runs through the armpit, the skin and nerve inflammation can be severe enough that the slight movement caused by breathing exacerbates the pain. Even simple skin inflammation from conditions like hidradenitis suppurativa can create localized nodules and tenderness that become painful when the skin folds are stretched.
When to Seek Emergency Medical Care
While many causes of armpit pain when breathing are minor, certain accompanying symptoms require immediate emergency medical attention. Any sudden, severe, or crushing chest pain that radiates into the arm, jaw, or back indicates a heart problem or a life-threatening pulmonary event, particularly if it feels heavy or tight.
Immediate care is necessary if the pain is accompanied by difficulty breathing, sudden shortness of breath, or a rapid and irregular heartbeat. Signs of poor oxygenation, such as blue discoloration of the lips or skin (cyanosis), also warrant urgent medical attention. New pain combined with high fever, chills, confusion, fainting, or coughing up blood suggests a severe infection or critical respiratory issue requiring prompt diagnosis and treatment.