The intermammary cleft is the visible groove or depression between the breasts, lying directly over the sternum (breastbone). In everyday language it is usually called cleavage, but in clinical and anatomical writing the term “intermammary cleft” (sometimes “intermammary sulcus”) refers to a specific anatomical region with its own nerve supply, lymphatic drainage, and susceptibility to particular skin and surgical problems. Understanding this small strip of real estate matters more than its size suggests, because it sits at a crossroads of breast surgery, dermatology, radiology, and even cancer staging.
What Defines the Region Anatomically
The intermammary cleft sits over the body of the sternum, roughly between the second and sixth ribs. The skin here is anchored more firmly to the underlying bone and fascia than the skin covering most of the breast mound, which is why the cleft holds its shape even when breast tissue is mobile. Beneath the skin lies a thin layer of subcutaneous fat, the sternal periosteum, and the origins of the pectoralis major muscles on either side. The fascia in this midline zone is an important surgical landmark: it is the tissue that keeps each breast pocket separate from the other, and its disruption is the root cause of a complication discussed further below.
Sensation along the cleft and the inner part of each breast comes predominantly from the anterior cutaneous branches of the intercostal nerves. The fourth intercostal nerve typically supplies the largest sensory territory in this area. In cadaveric mapping studies, the zone supplied by this single nerve measured up to 12 by 8 centimeters, covering substantial portions of the upper and lower inner quadrants of the breast.1PubMed Central. Intercostal nerve block of the anterior cutaneous branches and the sensibility of the female breast Damage to these nerve branches during surgery on or near the cleft can produce numbness or altered sensation across a surprisingly wide patch of skin.
Lymphatic Drainage and Cancer Staging
When breast cancer is diagnosed, surgeons map lymphatic drainage to figure out where cancer cells are most likely to spread first. Most of the breast drains toward the axilla (the armpit), and that is where sentinel-node biopsies are typically performed. But the inner portions of the breast, the tissue closest to the intermammary cleft, have a secondary drainage route: the internal mammary (also called internal thoracic) lymph node chain, which runs just behind the sternum alongside the internal mammary blood vessels.
Roughly 15 to 25 percent of total breast lymphatic drainage passes through this internal mammary pathway.2PubMed Central. Anatomy Versus Physiology: Is Breast Lymphatic Drainage to the Internal Thoracic (Internal Mammary) Lymphatic System Clinically Relevant? Inner-quadrant tumors drain to the internal mammary chain more frequently than outer-quadrant tumors. One large lymphoscintigraphy study found internal mammary drainage in about 37 percent of inner-quadrant lesions, compared with roughly 14 percent from outer quadrants.3PubMed Central. Lymphatic Drainage Patterns From the Breast
Despite the anatomical reality of this pathway, clinical practice has debated its relevance for decades. When researchers actually performed sentinel-node biopsies in a series of breast cancer patients, all 217 identified sentinel nodes turned up in the axilla, and none were found in the internal mammary chain, even though anatomy predicted two to four patients should have had them.4PubMed Central. Anatomy Versus Physiology: Is Breast Lymphatic Drainage to the Internal Thoracic (Internal Mammary) Lymphatic System Clinically Relevant? In separate imaging work using a small-particle radiotracer, internal mammary sentinel nodes were visualized in half of the patients, most often appearing in the second or third intercostal space.5PubMed Central. The Lymphatic Drainage Pattern of Internal Mammary Sentinel Lymph Node Identified by Small Particle Radiotracer (99mTc-Dextran 40) in Breast The gap between what imaging can show and what shows up during surgery means internal mammary node involvement is probably underdiagnosed. For tumors located near the intermammary cleft, this is especially worth knowing, because missing a positive node in this chain could change staging and treatment decisions.
Skin Problems That Target the Cleft
The intermammary cleft creates a warm, sometimes moist skin fold, and skin folds attract a specific set of dermatological problems. Intertrigo, an inflammatory rash caused by skin-on-skin friction and trapped moisture, is one of the most common. Candida (yeast) is the infectious agent most frequently responsible for intertrigo flares. Obesity, diabetes, and immunosuppressive conditions all raise the risk of both initial episodes and recurrence.6PubMed Central. Recurrent candidal intertrigo: challenges and solutions In people with larger breasts or during hot, humid weather, the cleft can stay damp enough throughout the day to provide an ideal environment for yeast overgrowth. Keeping the area dry, wearing breathable fabrics, and applying antifungal powder or cream at the first sign of redness are the standard first-line approaches.
The cleft and the wider V-shaped area of the upper chest are also a common site for poikiloderma of Civatte, a photoaging pattern that produces reddish-brown discoloration, broken blood vessels, and thinned skin. Dermoscopic studies of this condition have found converging curved blood vessels in about two-thirds of cases, linear irregular vessels in a similar proportion, and white macules in over 80 percent.7PubMed Central. Diagnosis and Differential Diagnosis of Poikiloderma of Civatte: A Dermoscopy Cohort Study The most common location was the V-shaped area of the chest, the same zone that tends to see chronic sun exposure when necklines are open. Unlike intertrigo, this is a cumulative sun-damage problem, and the cleft itself is often spared because the natural fold provides some shade, producing a characteristic pattern of discolored skin on either side with a pale strip in the middle.
Why Scars in This Area Often Heal Poorly
If you have ever seen a thick, raised scar on someone’s chest, it is not a coincidence that the sternum and cleft area are among the most common locations for keloids and hypertrophic scars. In a large study of keloid distribution, nearly half of all keloids (about 49 percent) occurred on the anterior chest, and another 27 percent on the scapular regions of the upper back.8PubMed. The relationship between skin stretching/contraction and pathologic scarring: the important role of mechanical forces in keloid generation The researchers noted that mechanical force appears to be a major trigger: these areas experience constant stretching and contraction from breathing, arm movements, and posture changes. Even in people genetically predisposed to keloids, the actual keloid formation clusters on high-tension sites.
This has practical implications if you are facing any surgery that involves an incision near or across the cleft, whether cardiac surgery through a median sternotomy, cosmetic procedures, or even the removal of a mole. Surgeons sometimes adjust incision placement or orientation to reduce tension on the final scar. Silicone sheeting, pressure garments, and early steroid injections are used post-operatively in people known to be prone to keloids, and the anterior chest is one of the areas where these precautions matter most.
Deep Sternal Wound Infections
The intermammary cleft sits directly over the sternum, so any surgery that involves splitting the breastbone puts this area at risk. Median sternotomy is one of the most common surgical approaches for open-heart procedures, and deep sternal wound infections are a serious complication. In a retrospective analysis of over 9,100 patients who underwent sternotomy at a single cardiac center, deep sternal wound infection occurred in about 2.3 percent of cases. Mortality in patients who developed this infection was nearly 10 percent, compared with roughly 3 percent in those who healed without complication.9Cor et Vasa. A retrospective analysis of deep sternal wound infections after longitudinal median sternotomy Treatment can involve vacuum-assisted closure systems and prolonged antibiotics, and in some cases the sternal bone remains intact while the soft tissue around it becomes infected.10Clinical Case Reports and Reviews. Alternative strategy for treating deep sternal wound infection following coronary artery bypass grafting with retention of the sternal plating system, systemic antibiotics, and vacuum assisted closure system: A case report For patients recovering from heart surgery, the intermammary cleft is not just a cosmetic landmark but a wound-care zone that requires careful monitoring.
Symmastia and the Loss of the Cleft
Symmastia is the clinical term for what happens when the intermammary cleft effectively disappears and the two breast mounds merge across the midline. The result sometimes gets called a “uniboob” or “breadloafing” in informal contexts. Symmastia can be congenital, but it is far more often iatrogenic, meaning it is caused by surgery.11PubMed. Surgical treatment of symmastia: A systematic review of techniques, outcomes and complications
During breast augmentation, the most common cause is detachment of the pectoralis major muscle from the sternum when implants are placed in a subpectoral pocket. Over-dissection of the medial breast pocket, choosing an implant whose base diameter is too wide for the chest, and disruption of the midline sternal fascia can all contribute.12Aesthetic Surgery Journal. Iatrogenic Symmastia: Causes and Suggested Repair Technique When the fascia that normally tethers skin and tissue to the sternum gives way, there is nothing to maintain the groove, and the implant or breast tissue migrates medially.
Repair is not straightforward. Published techniques involve reattaching Scarpa’s fascia to the sternum, reanchoring the pectoralis major, and often switching from a subpectoral to a different implant placement to avoid re-stretching the same tissue.13Aesthetic Surgery Journal. Iatrogenic Symmastia: Causes and Suggested Repair Technique Some surgeons use acellular dermal matrix or mesh to reinforce the midline. The revision rate for symmastia repair remains a concern, and patients considering breast augmentation should discuss cleft preservation with their surgeon, particularly if they have a naturally narrow intermammary distance.
Chest Wall Deformities and the Cleft
Pectus excavatum, the most common congenital chest wall deformity, changes the relationship between the breasts and the cleft. Because the sternum is depressed inward, the ribs on either side tilt, and the breasts often appear to slope medially, giving the impression that the intermammary distance is smaller than it actually is. A study evaluating women who underwent the modified Nuss procedure (a minimally invasive repair for pectus excavatum) found that correcting the skeletal deformity increased the distance between the nipples, confirming that the medially slanting breast appearance had been corrected by fixing the underlying bone structure.14PubMed Central. The changes of distance between nipples following correction of women pectus excavatum
For patients whose cleft area looks abnormal because of prominent ribs or residual asymmetry after skeletal repair, fat grafting has emerged as a soft-tissue solution. Injecting fat into the medial quadrants of the breast increases tissue thickness and can reduce an exaggerated intermammary gap or smooth out visible rib contours. Surgeons have reported that this approach improves symmetry in cases ranging from chest wall deformities to unilateral breast reconstructions.15Plastic & Reconstructive Surgery. Reply: Breast Cleavage Remodeling with Fat Grafting: A Safe Way to Optimize Symmetry and to Reduce Intermammary Distance
Garment-Related Skin Irritation
The intermammary cleft is one of the areas most affected by poorly fitting undergarments. Tight bras, particularly underwire styles, press directly against the sternum and the medial breast tissue for hours at a time. “Stretch garment dermatitis,” first described as a distinct condition caused not by chemical sensitization to fabrics or dyes but by pure mechanical pressure and friction from tight-fitting stretch garments like bras and girdles, can produce chronic irritation in this zone.16PubMed Central. Stretch garment dermatitis The condition is distinct from contact dermatitis caused by nickel in underwire or latex in elastic bands, though the two can overlap and be tricky to tell apart without patch testing. For anyone dealing with persistent redness or irritation along the cleft, switching to a wireless bra with a wider center gore, or sizing up, is a reasonable first step before pursuing a dermatological workup.
Imaging Blind Spots in the Medial Breast
The tissue closest to the intermammary cleft can be difficult to image thoroughly. Standard mammography compresses the breast from specific angles, and the most medial tissue, the part closest to the sternum, can fall outside the field of view. This problem extends to contrast-enhanced mammography (CEM), a newer technique that combines standard mammography with an iodine-based contrast agent to highlight areas of increased blood flow. One of the recognized disadvantages of CEM compared with MRI is the existence of blind spots that may not be captured by standard mammographic positioning, and the medial region of the breast is specifically identified as one of them.17PubMed. Contrast-enhanced Mammography Artifacts and Pitfalls: Tips and Tricks to Avoid Misinterpretation Breast MRI, which images the entire chest from a prone position, does not share this limitation. For patients with lesions suspected near the cleft or inner quadrant, MRI may provide better visualization.
Aesthetic Treatments for the Décolletage
The intermammary cleft and the surrounding décolletage see a fair amount of cosmetic attention. Sun damage, gravitational wrinkling, and thinning skin produce fine lines, crepiness, and discoloration across the upper chest over time. The skin here is thinner than on the face and has fewer sebaceous glands, which means it dries out faster and shows signs of aging earlier than many people expect.
Several treatment approaches target this region. Injectables like poly-L-lactic acid and hyaluronic acid fillers can address deeper rhytides (wrinkles), while energy-based devices such as fractionated lasers and microfocused ultrasound are used to tighten and resurface the skin.18Plastic and Reconstructive Surgery. Clinical Anatomy and Regional Approaches with Injectable Fillers: Décolletage Combination protocols have also shown promise. One approach using a triple treatment of botulinum toxin, hyaluronic acid, and energy-based skin tightening produced improvements in skin laxity and overall quality that patients rated as meeting or exceeding expectations.19PubMed Central. Diamond Technique: A Triple Treatment for Neck and Décolletage Rejuvenation Because the cleft and chest skin are prone to keloid scarring, ablative procedures need to be approached with caution: overly aggressive resurfacing can leave behind scars that are worse than the wrinkles they were meant to fix. The best candidates for chest resurfacing tend to be people with lighter skin tones and no personal history of abnormal scarring, though newer fractional devices have expanded the safety window somewhat.
Daily sunscreen on the chest is the single most effective preventive measure, and dermatologists increasingly emphasize that sunscreen should extend below the neckline whenever the décolletage is exposed. A silicone adhesive chest pad worn during sleep can also reduce overnight compression wrinkles, the vertical crease that forms when someone sleeps on their side and the breasts press together across the cleft. These sleep lines are different from photoaging lines and are largely mechanical in origin, which is why they respond to physical interventions rather than chemical ones.