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Pain Under Left Armpit: 16 Causes, When to Worry, and Treatments

Arms, Legs, Hands & FeetSymptoms & SignsConditions & Diseases
Pain Under Left Armpit: 16 Causes, When to Worry, and Treatments

Key points

  • Symptoms: Sharp or aching pain, tenderness, swelling, and pain that worsens with arm movement.
  • Resolution: Typically improves within a week with rest, ice, and gentle stretching.

Pain under the left armpit, also known as axillary pain, is a common complaint with a wide range of potential causes. The armpit is a complex junction of muscles, nerves, blood vessels, and a high concentration of lymph nodes. While most causes are benign and easily treatable, this discomfort can sometimes signal a more serious underlying condition.

This comprehensive guide synthesizes medical information and real-world experiences to help you understand the possible causes of pain under your left armpit, how to differentiate them, and when it's crucial to seek medical advice.

Common Causes of Left Armpit Pain

Most instances of armpit pain stem from issues related to the muscles, skin, or immune system response in the area.

Musculoskeletal Issues

The way you move and use your body can directly lead to pain in your armpit.

Muscle Strain

A pulled or strained muscle is one of the most frequent culprits. The muscles around your chest and shoulder, such as the pectoralis major or latissimus dorsi, can be injured during exercise, weightlifting, or even simple activities like reaching or twisting incorrectly.

  • Symptoms: Sharp or aching pain, tenderness, swelling, and pain that worsens with arm movement.
  • Resolution: Typically improves within a week with rest, ice, and gentle stretching.

Thoracic Outlet Syndrome (TOS)

This condition occurs when nerves or blood vessels in the space between your collarbone and first rib (the thoracic outlet) become compressed. According to the Hospital for Special Surgery, this can result from injury, repetitive arm movements, or anatomical defects.

  • Symptoms: Pain in the shoulder and armpit, neck pain, and numbness or tingling in the fingers.

!Anatomical illustration of the armpit showing muscles, lymph nodes, and nerves. An illustration of the complex anatomy within the armpit (axilla), including muscles, lymph nodes, and the brachial plexus nerves.

The sensitive skin of the armpit is prone to irritation and infection.

Allergic Reactions & Contact Dermatitis

Many personal care products can trigger a reaction. As noted by sources like Healthline and TODAY.com, common irritants include:

  • Deodorants and antiperspirants
  • Soaps and body washes
  • Laundry detergents
  • Lotions or perfumes

This results in an itchy, red, and painful rash.

Shaving and Hair Removal

Improper shaving with a dull or dirty razor can cause razor burn, ingrown hairs, and inflamed hair follicles (folliculitis), leading to painful bumps and irritation.

Infections (Bacterial and Fungal)

The warm, moist environment of the armpit is an ideal breeding ground for germs.

  • Bacterial Infections: Conditions like cellulitis or an abscess (boil) can cause significant pain, swelling, and redness.
  • Fungal Infections: Ringworm or intertrigo (a yeast infection in skin folds) can cause an itchy, painful rash.

Hidradenitis Suppurativa (HS)

This chronic inflammatory skin condition involves clogged hair follicles and sweat glands, leading to painful, recurring, pimple-like lumps or boils that can drain pus and cause scarring. It commonly affects areas where skin rubs together, like the armpits.

Lymphatic and Immune System Responses

Your armpit houses a large cluster of lymph nodes, which are key parts of your immune system.

Swollen Lymph Nodes (Lymphadenopathy)

When your body fights an infection—like the common cold, flu, or mono—your lymph nodes can swell and become tender, causing a dull, aching pain. This is a normal immune response.

Shingles

Shingles is a reactivation of the chickenpox virus, causing a painful, blistering rash that develops along a nerve path. If the affected nerve serves the armpit area, it can cause intense pain, tingling, or burning, sometimes even before the rash appears.

Less Common But Serious Causes

While less frequent, it's vital to be aware of serious conditions that can present with left armpit pain.

Cardiac Issues (Angina and Heart Attack)

Because of its proximity to the heart, pain under the left armpit can be referred pain from a cardiac event.

  • Angina: According to the American Heart Association, angina is chest pain caused by reduced blood flow to the heart. This discomfort can radiate to the shoulders, armpits, back, neck, and jaw.
  • Heart Attack: Armpit pain accompanied by chest pressure, shortness of breath, dizziness, and sweating is a medical emergency.

Cancer

In rare cases, armpit pain can be a sign of cancer. The American Cancer Society explains that cancers like breast cancer, lymphoma, and lung cancer can cause the axillary lymph nodes to swell, leading to a persistent lump or pain. Sometimes, this pain is the first noticeable symptom.

Special Considerations and Unseen Factors

Some causes of armpit pain are less obvious and often overlooked.

Can Anxiety Cause Armpit Pain?

Yes, anxiety can be a direct and indirect cause of armpit pain. Forum discussions, like those on Reddit, highlight how this happens:

  • Muscle Tension: Chronic anxiety often leads to unconscious and prolonged tensing of muscles in the shoulders, neck, and chest, which can cause aching pain in the armpit.
  • Hypervigilance: Anxiety can make you hyper-aware of normal bodily sensations, causing minor aches to feel more intense and alarming.

Armpit Pain with No Lump

Experiencing pain without a noticeable lump can be confusing. Common causes include:

  • Muscle strain: The injury is in the muscle tissue itself, not forming a lump.
  • Nerve irritation: Pinched or inflamed nerves can cause pain without a visible sign.
  • Referred pain: The source of the pain is elsewhere, such as the heart or spine.
  • Early-stage infection or inflammation: Pain can begin before significant swelling or a lump develops.

!A woman experiencing armpit pain, holding her arm in discomfort. Discomfort in the armpit can interfere with daily activities and warrants attention.

Gender-Specific Concerns (Primarily in Females)

While most causes affect everyone, some are more specific to women.

  • Hormonal Changes: Breast tissue can extend into the armpit (the tail of Spence). Cyclical breast pain related to the menstrual cycle can therefore be felt as armpit pain.
  • Breast Infections (Mastitis): Especially common in breastfeeding women, this infection can cause pain, swelling, and redness that extends to the armpit.
  • Breast Cancer: As mentioned, swollen axillary lymph nodes are a key sign of breast cancer spread. Regular self-checks of both the breast and armpit area are crucial.

When to See a Doctor

While many cases of armpit pain resolve on their own, Medical News Today and other health authorities advise seeking medical attention if you experience any of the following:

  • Sudden, severe pain, especially with chest pain, shortness of breath, dizziness, or sweating—call 911 immediately.
  • Pain that lasts for more than a week without improvement.
  • A lump that is hard, doesn't move, or is getting larger.
  • Signs of a worsening infection, such as high fever, spreading redness, or pus.
  • Unexplained weight loss, fever, or night sweats.
  • Pain that interferes with your daily activities or sleep.

Diagnosis and Treatment

A doctor will diagnose the cause of your pain through a combination of a physical exam and a review of your medical history.

How Armpit Pain is Diagnosed

Based on the initial assessment, your doctor may order tests, including:

  • Blood tests to check for signs of infection or autoimmune disease.
  • Imaging scans like an ultrasound, MRI, or mammogram to look at soft tissues and lymph nodes.
  • A biopsy, where a small tissue sample is removed from a lump or lymph node to be tested for cancer.
  • Allergy testing (patch tests) to identify contact dermatitis triggers.

Treatment Approaches

Treatment is tailored to the underlying cause:

  • Muscle Strains: Rest, ice, compression, and elevation (R.I.C.E.). Over-the-counter pain relievers like ibuprofen can help.
  • Infections: Topical or oral antibiotics or antifungal medications.
  • Skin Irritation: Identifying and avoiding the irritant and using soothing creams.
  • Swollen Lymph Nodes: Treating the underlying infection or illness.
  • Serious Conditions: Treatment for conditions like cancer, heart disease, or TOS requires specialized medical care, which can range from medication to surgery.

References

Michael O'Connell, DO

About the author

Michael O'Connell, DO
Emergency Medicine Physician

Michael O'Connell, DO, is a board-certified emergency medicine physician working as an attending physician at a busy Level I Trauma Center in Philadelphia, Pennsylvania. He also serves as a clinical instructor for medical residents and is active in wilderness medicine.