What Is a Sinus Tract? Causes, Symptoms, and Treatment

A sinus tract is an abnormal channel that forms between an infected or inflamed area deep inside the body and an opening on the skin’s surface. Think of it as a narrow tunnel the body creates to drain pus or fluid from a pocket of infection that has nowhere else to go. Unlike a fistula, which connects two internal body cavities or organs, a sinus tract has only one opening, typically on the skin, while its other end terminates in the infected tissue itself. These tracts can appear almost anywhere on the body, from the face and jaw to the tailbone, abdominal wall, or even the spine, and their causes range from dental infections to surgical complications to congenital defects.

How a Sinus Tract Forms

The body builds a sinus tract through a surprisingly logical process. When infection or chronic inflammation sits deep in tissue and cannot resolve on its own, pressure from accumulating pus or fluid pushes outward along the path of least resistance. Over days, weeks, or sometimes months, that pressure carves a narrow channel through soft tissue toward the skin surface. Once it breaks through, you get an opening that drains on and off, sometimes for years if the underlying cause is not addressed.

The channel itself becomes lined with a mix of inflamed and granulation tissue, which is the body’s repair tissue. In dental sinus tracts, for example, the channel extends from an infected tooth root to the face or neck, with its exact path influenced by how close the tooth’s root tip sits to the surrounding bone, muscle attachments, and jaw shape.¹ When the tract opens outside the mouth onto the skin of the face, it leaves behind a small dimple or nodule that can easily be mistaken for a skin condition, leading patients to dermatologists before anyone thinks to check their teeth.

Common Causes

Sinus tracts do not appear out of nowhere. There is always an underlying source feeding them, and identifying that source is the key to treatment. The most common drivers fall into a few broad categories.

Dental Infections

Tooth-related infections are one of the most frequent causes. When a tooth dies or becomes severely decayed, bacteria colonize the root canal system and eventually spread beyond the root tip into the surrounding bone. A study examining teeth associated with sinus tracts found that the vast majority had bacteria not just inside the root canal but also outside it, adhering to the outer root surface or sitting in the surrounding tissue.² That dual infection, inside and outside the root, explains why these tracts tend to persist until the tooth is properly treated or extracted. The tract itself is the body’s pressure-relief valve for the ongoing abscess.

Retained Foreign Bodies

Anything the body cannot break down or absorb can trigger a chronic inflammatory reaction that eventually forms a sinus tract. Surgical materials are a common culprit. Leftover suture material, mesh used in hernia repairs, or bone graft particles can all provoke the body’s immune system into forming a walled-off pocket of inflammation that eventually tunnels to the skin.³ One case report documented a sinus tract on the face that formed after a bone graft material used in facial surgery triggered a chronic foreign body reaction, requiring surgical removal of both the tract and the residual graft particles.⁴ These foreign body sinus tracts are particularly frustrating because they will not heal until every last bit of the offending material is removed.

Bone Infections

Chronic osteomyelitis, a persistent infection of bone, frequently produces sinus tracts that drain through the overlying skin. The infection smolders in the bone for months or years, and the tract serves as a chronic drainage pathway. One important clinical detail about osteomyelitis-related tracts: swabbing the drainage from the skin opening does not reliably identify the actual bacteria causing the bone infection. A classic study found that only about 44% of sinus tract cultures matched the organism found during surgery on the bone itself.⁵ The skin opening picks up contaminating bacteria from the skin surface, which muddies the diagnostic picture.

Skin and Soft Tissue Conditions

Hidradenitis suppurativa, a chronic inflammatory skin disease, is notorious for producing interconnected sinus tracts, often called tunnels, in areas like the armpits, groin, and under the breasts. The disease starts with inflammation around hair follicles, possibly triggered by a structural defect where the oil gland connects to the hair follicle, followed by bacterial colonization.⁶ Over time, these inflamed areas burrow under the skin and link up, forming networks of tracts that drain intermittently. Research has shown that these tunnels become lined with skin-like tissue and harbor intense inflammation, including immune cells and inflammatory signals similar to those seen in psoriasis.⁷ That self-sustaining inflammatory environment is part of why the disease is so difficult to treat.

Where Sinus Tracts Appear on the Body

The location of a sinus tract often gives the first clue about its cause. While they can theoretically form anywhere there is soft tissue, certain sites come up again and again in clinical practice.

The Tailbone Area

Pilonidal sinus tracts form in the cleft between the buttocks, usually near the tailbone, and are especially common in young adults. They develop when loose hairs burrow into the skin and trigger a foreign body reaction. The body walls off the hair with a granuloma, a ball of inflamed tissue, which then creates a tract to the skin surface through partially skin-lined openings.⁸ These can flare into painful abscesses or drain chronically with foul-smelling fluid. People who sit for long periods, have coarse body hair, or have a deep natal cleft are at higher risk.

The Face and Neck

Dental sinus tracts that exit through the skin of the face are a well-known diagnostic trap. The opening can appear on the chin, cheek, or along the jawline, and it often looks like a stubborn pimple or skin lesion. Patients frequently see dermatologists or general practitioners first, and the dental origin can go unrecognized for months or even years. When the tract opens outside the mouth rather than inside it, healing typically leaves a visible scar.⁹ Pain and drainage from these facial lesions can range from barely noticeable to quite bothersome, with some patients reporting intermittent bloody or pus-like discharge.¹⁰

In Front of the Ear

Preauricular sinuses are a different animal entirely. These are congenital, meaning you are born with them, and they appear as tiny pits or dimples just in front of the ear. Most of the time they cause no symptoms at all. They can be inherited in an autosomal dominant pattern and are bilateral in roughly a quarter to half of cases. In a small percentage of people, roughly 3 to 10%, they are associated with other conditions, including hearing loss and branchio-oto-renal syndrome.¹¹ Problems arise only when the sinus becomes infected, at which point it can form an abscess that requires drainage or surgical removal.

The Spine

Spinal dermal sinus tracts are rare congenital tracts that extend from the skin of the back inward toward the spinal cord. They present as a small pit or dimple on the lower back, sometimes with a tuft of hair around it. Unlike the other types discussed here, these carry the risk of serious neurological complications, including bacterial meningitis or infection of the spinal cord, because the tract provides a direct route for bacteria to reach the central nervous system. MRI is the definitive way to diagnose them, and complete surgical removal of all tract tissue is necessary to prevent recurrence.¹²

The Abdominal Wall

After abdominal surgery, sinus tracts can form if retained suture material, mesh, or other surgical debris triggers a chronic reaction. These tracts connect the deep surgical site to the skin surface and drain intermittently. They are considered rare but are probably underrecognized, particularly when the connection to the original surgery is not immediately obvious.¹³

Signs and Symptoms

The hallmark of a sinus tract is a small opening on the skin that drains intermittently. What comes out can range from thin, watery fluid to thick pus, sometimes with blood mixed in. Many people describe the discharge as foul-smelling, and the skin around the opening may be red, swollen, or tender. Some tracts drain so little that the opening looks like nothing more than a persistent dimple or pimple that never quite heals. Others are more dramatic, with periodic flare-ups of pain, swelling, and copious drainage followed by quiet periods.

Beyond the physical symptoms, chronic sinus tracts take a real toll on quality of life. Research on patients with chronic wounds, including draining sinus tracts, has documented reduced mobility, persistent pain and discomfort, sleep problems, social isolation, anxiety, and depression. The presence of an ongoing wound can affect body image, relationships, and the ability to work or carry out daily activities.¹⁴ This psychological burden is sometimes overlooked in favor of focusing purely on the physical wound, but it matters, particularly for people living with conditions like hidradenitis suppurativa where tracts can persist for years.

How Doctors Track Down the Source

Finding the sinus tract opening is usually easy. Figuring out where it leads and what is feeding it is the harder part. A thorough physical examination is the starting point. For dental sinus tracts, a dentist may trace the tract by gently inserting a thin, flexible probe called a gutta-percha point through the opening and then taking an X-ray to see which tooth the probe leads back to. For abdominal wall tracts, imaging is essential. CT sinography, where contrast dye is injected into the tract before a CT scan, significantly outperforms conventional X-ray-based sinography. One study found that CT sinography had an accuracy of about 85% for determining how far the tract extended, compared to roughly 60% for X-ray sinography.¹⁵ The CT approach was also substantially better at identifying whether the tract had formed a fistula connecting to the abdominal cavity.

For spinal dermal sinus tracts, MRI is the imaging method of choice because it provides the detailed soft-tissue contrast needed to see whether the tract communicates with the spinal canal. And for bone-related sinus tracts, clinicians need to remember that swab cultures from the skin opening are unreliable. As noted in the osteomyelitis research, the bacteria growing at the surface opening often do not match what is actually causing the deep infection.⁵ When the correct antibiotic choice matters, a surgical bone biopsy or deep tissue sample is far more trustworthy.

Treatment

The single most important principle of sinus tract treatment is addressing the underlying source. Antibiotics alone will not close a tract if a dead tooth, a piece of retained suture, or a smoldering bone infection is still present. The tract is a symptom, not the disease, and it will keep reforming until its fuel source is eliminated.

Dental Sinus Tracts

For tracts originating from infected teeth, root canal treatment or extraction of the offending tooth is the standard approach. Once the source of infection is removed, the tract typically closes on its own within a few weeks. When the tract opens onto the facial skin, however, the resulting scar may require a minor cosmetic procedure later.

Surgical Excision

Many sinus tracts, particularly those caused by foreign bodies, osteomyelitis, or congenital defects, require surgical removal. The goal is to excise the entire tract along with any foreign material, infected bone, or cyst at its deep end. Incomplete removal is the main driver of recurrence. For pilonidal sinuses, excision followed by primary closure on the same day has been shown to be safe and effective as a day-surgery procedure.¹⁶ When the wound is too large for immediate closure, negative pressure wound therapy can help. In one case involving a very large pilonidal excision, negative pressure therapy was applied for about a month, followed by standard wound care, with complete healing by 90 days.¹⁷

Laser-Based Approaches

Minimally invasive laser treatments have gained traction for pilonidal sinus tracts in particular. These procedures involve threading a laser fiber into the tract and using thermal energy to destroy the lining from the inside, allowing the tract to collapse and heal. One study using a 1470-nm radial diode laser in 48 patients reported a 100% healing rate with an average healing time of about four weeks and a recurrence rate of only about 2%.¹⁸ A larger multicentre study of laser-assisted sinus closure found somewhat different results: an initial success rate of about 66% after a single treatment, rising to over 90% after a second procedure and 98% after a third. The average time to return to normal daily activities was six days, and most patients needed only over-the-counter pain relief or nothing at all.¹⁹ Combining laser treatment with phenol application may further reduce recurrence, with one study finding recurrence in fewer than 5% of patients who received the combined approach.²⁰

The appeal of laser treatment is clear: smaller wounds, less pain, and faster recovery. But the evidence suggests it sometimes takes more than one session, and a small number of patients still end up needing conventional surgery afterward.

Preauricular Sinus Surgery

For preauricular sinuses that become repeatedly infected, surgical excision is the definitive treatment. The recurrence rate after surgery is generally low, around 5% in one study, but the choice of anesthesia appears to matter. That same study found that procedures done under local anesthesia had a significantly higher recurrence rate than those done under general anesthesia, possibly because inadequate visualization or patient discomfort under local anesthesia leads to incomplete excision.²¹

Why Sinus Tracts Come Back

Recurrence is the persistent frustration with sinus tracts of all types. The most common reason is incomplete removal of the underlying cause: a fragment of foreign material left behind, a tooth root not fully cleaned out, a sliver of tract lining that survives to regenerate. For pilonidal sinuses specifically, factors like obesity, a deep natal cleft, poor wound hygiene, and the presence of coarse hair in the area all contribute to the tract returning.²² Surgeons have long debated whether the wound should be closed immediately after excision or left open to heal from the bottom up, and there is no single answer that fits every patient.

For hidradenitis suppurativa, recurrence is almost expected because the disease itself is chronic and systemic. Excising one set of tracts does not stop new ones from forming elsewhere. Treatment in these cases often involves a combination of surgery for existing tracts and ongoing medical therapy, including biologic medications, to suppress the underlying inflammation.

When a Sinus Tract Is Not What It Seems

One of the trickiest aspects of sinus tracts is that they often mimic other conditions. A dental sinus tract on the chin looks like a skin cyst or a chronic pimple. A pilonidal sinus can be mistaken for a simple boil. A draining preauricular sinus gets confused with an ear infection. And a spinal dermal sinus may be dismissed as an unremarkable dimple on a newborn’s back until neurological symptoms appear.

The misdiagnosis problem runs the other direction too. Some skin conditions that look like sinus tracts are not. A chronic draining wound from an underlying cancer, for instance, can mimic an infectious sinus tract. Crohn’s disease can produce perianal fistulas and tracts that resemble pilonidal disease but require entirely different management. The diagnostic workup described earlier, especially imaging with CT sinography or MRI, exists precisely because the surface appearance of these tracts tells you very little about what is happening underneath. If you have a skin opening that drains, does not heal, and keeps coming back after superficial treatment, the answer almost always lies deeper than the skin itself.