What is the muscle under my breast called? A guide to chest wall anatomy

October 2, 2025 •

3 min read

According to the National Institutes of Health, the pectoralis major is the largest and most superficial muscle on the anterior chest wall, lying directly underneath the breast tissue. Understanding the roles of the pectoralis major and other surrounding muscles helps explain what is the muscle under my breast called and how it functions in daily movement and breathing.

Quick Summary

The pectoralis major is the primary muscle beneath the breast, with the smaller pectoralis minor situated deeper beneath it. Other muscles like the serratus anterior and intercostals also comprise the chest wall. Pain in this area can stem from muscle strain, inflammation (costochondritis), or more serious underlying conditions, so a proper diagnosis is key.

Key Points

Pectoralis Major: The large muscle directly under the breast tissue, essential for arm movements.
Pectoralis Minor: A smaller muscle beneath the pectoralis major, stabilizing the shoulder blade.
Other Muscles: The chest wall includes the serratus anterior and intercostal muscles, involved in movement and breathing.
Costal Cartilage: Connects ribs to the breastbone; inflammation is costochondritis.
Causes of Pain: Can include muscle strain, costochondritis, or referred pain from other organs.
When to See a Doctor: Seek immediate medical attention for severe, sudden, or radiating chest pain, especially with other serious symptoms.

The Pectoralis Major and Pectoralis Minor: The Primary Chest Muscles

The most prominent muscle directly beneath the breast is the pectoralis major. This large, fan-shaped muscle covers the upper part of the chest wall and plays a significant role in movements of the arm and shoulder. Below the pectoralis major lies another, smaller muscle known as the pectoralis minor.

Pectoralis Major

Often called the 'pec' muscle, the pectoralis major is located on each side of the chest and is divided into two heads: a clavicular head (originating from the collarbone) and a sternocostal head (originating from the breastbone and ribs). The fibers from both heads converge and attach to the humerus, the bone of the upper arm.

This muscle is responsible for a variety of powerful upper-body movements, including adduction, flexion, and internal rotation of the arm.

Pectoralis Minor

The pectoralis minor is a thin, triangular muscle located underneath the pectoralis major. It originates on the ribs and inserts into the scapula (shoulder blade). It is an important stabilizing muscle for the shoulder complex, helping to keep the shoulder blade pressed against the chest wall and assisting in moving the shoulder forward.

Beyond the Pectoral Muscles: Other Chest Wall Anatomy

The chest wall is a complex structure involving more than just the pectoral muscles. Other muscles in the area can contribute to movement, breathing, and potential discomfort.

Serratus Anterior

Located on the side of the chest, wrapping around the rib cage, the serratus anterior is sometimes called the 'boxer's muscle' because it helps pull the scapula forward during movements like throwing a punch.

Intercostal Muscles

These muscles lie between the ribs and are vital for breathing. The external intercostals help expand the rib cage during inhalation, while the internal intercostals aid in forced exhalation.

The Diaphragm

The diaphragm is a large, dome-shaped muscle beneath the chest cavity that is the primary muscle of breathing. It contracts to draw air into the lungs.

The Role of Costal Cartilage

Costal cartilage connects the ribs to the breastbone (sternum), providing flexibility to the rib cage for breathing. Inflammation of this cartilage is called costochondritis, which can cause pain under the breast.

Potential Causes of Pain Under the Breast

Pain under the breast can have various causes, from muscle issues to more serious conditions. A proper diagnosis from a healthcare provider is essential for persistent or severe pain.

Potential causes include:

Muscle Strain: Overuse of pectoral or intercostal muscles.
Costochondritis: Inflammation of costal cartilage.
Gastrointestinal Issues: Conditions like acid reflux.
Heart-Related Problems: Though less common, conditions like angina. Seek immediate medical attention for sudden, severe chest pain radiating to the arm, neck, or back.

Comparison of Pectoralis Major and Minor


Feature	Pectoralis Major	Pectoralis Minor
Location	The largest and most superficial muscle on the chest.	A smaller, triangular muscle located deep to the pectoralis major.
Origin	Medial half of the clavicle, sternum, and upper six costal cartilages.	Anterior surfaces of the 3rd, 4th, and 5th ribs.
Insertion	Inserts into the lateral lip of the bicipital groove of the humerus.	Inserts into the coracoid process of the scapula.
Primary Function	Adduction, flexion, and internal rotation of the arm.	Stabilizes the scapula against the chest wall.
Associated Pain	Pain may result from strenuous exercises.	Can be prone to tightness.

Conclusion

To answer what is the muscle under my breast called?, the primary muscle is the pectoralis major, a large muscle vital for arm movements. Beneath it are the pectoralis minor, serratus anterior, and intercostal muscles, which are also important for arm function and breathing. Pain in this region can be caused by muscle strain, costochondritis, or referred pain from other organs. Understanding this anatomy helps in identifying discomfort. Consult a medical professional for guidance when necessary, based on information from the Hospital for Special Surgery.

Frequently Asked Questions

Yes, a strained or overstretched pectoral or intercostal muscle can cause soreness and pain under the breast. This is a common cause of chest pain, often resulting from physical activities like lifting heavy objects or performing repetitive motions.

Costochondritis is an inflammation of the cartilage that connects your ribs to your breastbone. This condition can cause sharp or aching pain that is felt in the chest and can radiate to the area under the breast, often worsening with deep breaths or coughing.

The pectoralis major is the large, superficial muscle that forms the bulk of the chest. The pectoralis minor is a smaller, triangular muscle located deeper, beneath the pectoralis major. The major muscle controls arm movement, while the minor muscle stabilizes the shoulder blade.

Yes, the underlying musculature of the chest wall, including the pectoralis major and pectoralis minor, is structurally the same in both men and women. The primary difference is the presence of breast tissue, which consists of glandular and fatty tissue, and its anchoring ligaments.

While many causes are benign, you should seek immediate medical attention for severe, sudden, or radiating chest pain, especially if accompanied by shortness of breath, cold sweats, or dizziness, as these could be symptoms of a heart attack or other serious condition.

The serratus anterior is a fan-shaped muscle located on the side of the chest, wrapping around the rib cage. It works with the pectoral muscles to move the scapula and can also act as an accessory muscle for breathing.

Yes, the intercostal muscles located between your ribs and the diaphragm muscle at the base of your chest are crucial for breathing. Problems or inflammation in these muscles, such as with costochondritis, can cause pain and affect your ability to breathe deeply.