The area between your breasts is formally called the intermammary cleft, sometimes written as the intermammary sulcus in medical texts. Most people know it as “cleavage,” while the broader visible chest area above and between the breasts is often called the décolletage. What makes this patch of skin anatomically distinct from the breast tissue on either side is what lies directly beneath it and the particular way the skin behaves there, both of which matter for everything from bra fitting to skin care to surgery.
What Lies Beneath the Intermammary Cleft
Directly under the skin of the intermammary cleft sits the sternum, your flat breastbone. A layer of dense connective tissue called the presternal fascia anchors the skin to the bone more firmly here than almost anywhere else on the torso. That tight adhesion is what creates the visible valley between two breasts: the breast mounds, made largely of fat and glandular tissue, drape laterally over the ribcage, but the midline skin stays tethered down. This is why, even in people with larger breasts, the center of the chest remains relatively flat unless something disrupts that natural attachment.
The skin over the sternum is also thinner than the skin covering the breast mounds themselves. It has fewer subcutaneous fat deposits and sits on a hard, bony surface, which means it can be more sensitive to pressure from underwire bras or surgical manipulation. The connective-tissue anchor is relevant in both cosmetic surgery and in understanding a condition called symmastia, which we will get to shortly.
Why Skin Problems Love This Spot
The intermammary cleft and the folds just beneath each breast create a warm, enclosed microenvironment that is ideal for skin irritation. Apocrine sweat glands, which produce a thicker secretion than ordinary sweat glands, are concentrated in the breasts along with the underarms, face, and scalp.1PubMed Central. Physiology of sweat gland function: The roles of sweating and sweat composition in human health When sweat gets trapped between the breasts, the combination of moisture, heat, and skin-on-skin friction sets the stage for a group of conditions collectively known as intertrigo.
Intertrigo is not a single disease but a pattern of irritation that affects skin folds anywhere on the body. In a study examining where fungal and related skin infections tend to cluster, the groin was the most common site, followed by the spaces between toes, the underarms, and the inframammary folds (the creases just below the breasts).2PubMed Central. Investigation of Intertriginous Mycotic and Pseudomycotic (Erythrasma) Infections and Their Causative Agents with Emphasize on Clinical Presentations The intermammary cleft itself sits right at the top of those inframammary folds, so when redness, itching, or a yeast-like rash appears “between the breasts,” it often starts at the fold and creeps upward.
Common culprits include candidal yeast, dermatophyte fungi, and a bacterial condition called erythrasma that produces a coral-pink discoloration visible under ultraviolet light. Practical prevention is straightforward: keeping the area dry, using a moisture-wicking fabric against the skin, and applying an antifungal powder or barrier cream during hot weather or heavy exercise. People with larger breasts, those who exercise frequently, or anyone living in a humid climate tend to experience these problems more often simply because the microclimate between and beneath the breasts stays warmer and wetter for longer.
Sensation and Nerve Supply
The skin of the intermammary cleft and inner breast quadrants gets its feeling mainly from the anterior cutaneous branches of the intercostal nerves, particularly the third and fourth. In anatomical mapping of these nerves, the fourth intercostal nerve supplied the largest individually innervated zone on the breast, covering an area roughly the size of a palm and centered over the upper and lower inner quadrants. The third intercostal nerve supplied the second-largest zone, also in the inner quadrants.3PubMed Central. Intercostal nerve block of the anterior cutaneous branches and the sensibility of the female breast
This matters practically in two situations. First, during breast surgery or chest procedures, surgeons need to preserve or account for these nerve branches to minimize numbness. Second, the concentration of nerve supply in the inner breast explains why many people find the medial breast tissue and the intermammary cleft particularly sensitive to touch, temperature, and irritation. Pain or tenderness in this area can sometimes be mistaken for cardiac-related chest pain, since the sternum sits right behind it, though the sensation is actually originating in the skin and intercostal muscles rather than the heart.
Symmastia and When the Cleft Disappears
One of the more unusual conditions affecting this area is symmastia, in which the two breast mounds merge across the midline and the normal cleft between them vanishes. Symmastia is defined as a confluence of the breast mounds across the mid-sternal line, with the skin losing its normal adhesion to the sternum underneath.4PubMed. Surgical treatment of symmastia: A systematic review of techniques, outcomes and complications The result looks like a single connected breast tissue shelf stretching across the chest, sometimes described colloquially as a “uniboob” or “breadloafing.”
Congenital symmastia, present from birth, is extremely rare. The far more common form is iatrogenic, meaning it happens as a complication of breast augmentation surgery. When an implant pocket is dissected too far toward the midline, or when thin presternal tissue gives way under the pressure of an implant, that tight fascial anchor we talked about earlier breaks down. The implant migrates medially, and the skin lifts off the sternum. Correcting it usually requires rebuilding the internal pocket, sometimes with acellular dermal matrix or internal sutures, to re-establish the boundary the original surgery disrupted.
Intermammary Distance and Cosmetic Goals
Even outside the context of symmastia, the width of the intermammary cleft is one of the measurements cosmetic surgeons think about carefully during breast augmentation. The intermammary distance, measured from the medial border of one breast to the medial border of the other, varies naturally depending on chest width, breast shape, and how the breast tissue is distributed. Some people have naturally wide-set breasts with a broad, flat cleft, while others have breasts that nearly touch at the midline.
A 2024 study found that the intermammary distance can be safely reduced using implants alone, without fat grafting, through precise dissection of the medial pocket. Micropolyurethane foam-coated implants helped keep the device stable during healing and prevented the kind of medial migration that can lead to symmastia.5PubMed. Safe Reduction of Intermammary Distance in Implant Breast Augmentation Without Fat Grafting The tricky part is that surgeons have to walk a fine line: moving the implant too far medially risks detaching the presternal skin from the sternum, but stopping too far laterally leaves a wider gap than the patient wanted. The natural anatomy of the cleft, specifically how thick and firmly attached the presternal fascia is, sets the limit on how much the distance can be narrowed.
How Bra Design Shapes the Cleft
If you have ever wondered why different bras produce dramatically different-looking cleavage, the answer lives in a small piece of fabric and wire you might not have thought much about: the gore. The gore is the center panel of a bra, the strip of material that sits flat against the sternum and bridges the two cups. Its height, width, and stiffness determine how much the cups push the breasts together or hold them apart.
Finite element modeling of bra-breast interaction has shown that the length of the upper portion of the gore positively contributes to gathering the breasts toward the midline and creating a deeper-looking cleavage, while the length of the lower gore has more to do with the lifting effect and the position of the underwire.6Industria textila. Utilising finite element analysis to evaluate gore design in bras A taller upper gore pushes the medial breast tissue closer together; a taller lower gore lifts the breast upward but does not create as much medial compression.
The choice between underwired and wireless designs also makes a measurable difference. Simulations have confirmed what most bra-wearers already sense intuitively: an underwired bra produces more pronounced lifting, gathering, and forward projection of the breast than a wireless one. The shaping effect of a wireless bra was roughly three-fifths of what an underwired bra achieved.7Computer-Aided Design. 3D bra and human interactive modeling using finite element method for bra design That trade-off matters because the same forces that create a more dramatic cleavage also increase pressure at the gore, the underwire, and the shoulder straps. Stiffer cup materials and higher-tension straps raise contact pressure across the board, which can lead to discomfort over time.8Textile Research Journal. 3D finite-element-based orthogonal design for optimization of adjustable bras with pressure fit and shaping effect
For anyone frustrated by a gore that refuses to sit flat against the sternum, the usual cause is a cup size that is too small, forcing the center panel outward, or a band that is too loose, letting the whole bra ride forward. A properly fitting bra should have the gore resting flush against the intermammary cleft with no gap. When it does, the breast tissue stays in the cups rather than migrating under or over the wire, which also reduces the friction and sweating issues described earlier.
Breast Skin Strain During Exercise
The intermammary cleft is not just an aesthetic landmark; the skin there stretches and rebounds every time the breasts move. And the breasts move a lot during exercise. Bare-breasted peak skin strain on the breast increases from about 31% during quiet standing to 36% while walking and 46% while running.9BMJ Open. Do static and dynamic activities induce potentially damaging breast skin strain? Most people stayed below the 60% threshold considered potentially damaging to skin, but several participants exceeded it during running, with peak strains as high as 93% in one case.
Perhaps more striking than the peak strain itself was the rate at which it occurred. The peak strain rate jumped more than fourfold between walking and running, meaning the skin was being stretched much more abruptly, not just more extensively. That rapid, repeated stretching is what contributes to the gradual loss of skin elasticity and the development of stretch marks over time, particularly in the medial and inferior breast regions where Cooper’s ligaments anchor the breast to the chest wall. A well-fitting sports bra reduces both the magnitude and the rate of breast skin strain, which is why breast biomechanics researchers consistently emphasize bra support for high-impact activities.
Sun Damage on the Chest
The upper chest and décolletage, including the intermammary cleft, are among the body’s most sun-exposed surfaces for anyone who wears V-neck or scoop-neck clothing. Over years, cumulative UV exposure produces what dermatologists call poikiloderma of Civatte, a mottled reddish-brown discoloration with a net-like pattern of tiny blood vessels and pigment changes. This is one of the most common cosmetic complaints related to the chest area, and it is often mistaken for a rash or allergic reaction when people first notice it.
Distinguishing sun-induced poikiloderma from other conditions that can appear in the same location requires some clinical context. A different pattern of red dots in a net-like arrangement has been documented on the upper chest in association with certain forms of scarring hair loss, and that pattern is distinguished from sun damage by its abrupt onset, accompanying itchiness, and the absence of a significant sun-exposure history.10Skin Appendage Disorders. Red Dots in a Net-Like Pattern on the Upper Chest: A Novel Clinical Observation in Frontal Fibrosing Alopecia and Fibrosing Alopecia in Pattern Distribution For the more common, slow-developing sun damage pattern, prevention comes down to sunscreen applied consistently to the chest, not just the face. Treatment options include pulsed-dye lasers for redness and intense pulsed light for pigmentation, though results are gradual and often require multiple sessions.
Why Humans Have a Visible Cleft at All
The intermammary cleft as a recognizable feature exists only because human breasts are permanently enlarged, even outside of pregnancy and nursing. That is a genuinely unusual trait among primates. Other mammals develop swollen breast tissue only during lactation. Permanently enlarged, fat-filled breasts that appear at puberty and persist for life are unique to humans, and evolutionary biologists have debated why for decades.11PubMed. The evolution of perennially enlarged breasts in women: a critical review and a novel hypothesis
Proposed explanations have ranged from sexual selection (breasts as an honest signal of reproductive fitness) to functional hypotheses (fat reserves for nursing, thermoregulation, or infant feeding mechanics). A more recent proposal suggests that permanent breast tissue may have appeared as early as Homo ergaster, not as a direct adaptation but as a by-product of other evolutionary changes happening simultaneously, such as increased subcutaneous fat storage and changes in body composition. Whatever the reason, the visible cleft between the breasts is a secondary consequence of having two distinct mounds of adipose tissue sitting on either side of a bony midline. Without permanent breast tissue, there would be no cleft to name.
Terminology the Reader Will Encounter Elsewhere
Depending on the context, you may run into a handful of overlapping terms for essentially the same area. “Intermammary cleft” and “intermammary sulcus” are the clinical anatomy terms and tend to appear in surgical literature. “Cleavage” is the everyday English word and also shows up in fashion and lingerie contexts. “Décolletage” technically refers to the entire area of the upper chest, neck, and shoulders exposed by a low neckline, so it includes but is not limited to the cleft. In dermatology papers, you might see “presternal skin” or “mid-sternal region,” which describe the same surface from a skin-care perspective rather than a breast-anatomy one.
In bra fitting, the relevant term is the “gore” or “bridge,” which is the part of the garment designed to sit against this area. And in cosmetic surgery, “intermammary distance” is the clinical measurement from one breast’s inner border to the other, effectively quantifying the width of the cleft. None of these terms are wrong; they just reflect different professions approaching the same anatomical real estate from different directions.