Understanding Pyoderma Gangrenosum

Pyoderma gangrenosum (PG) is a rare and often misunderstood inflammatory skin condition that causes painful, non-healing ulcers. If you are reading this, you may be dealing with an ulcer that appeared suddenly or grew rapidly, causing intense pain that feels out of proportion to what you can see on the surface. It is important to know that despite its name, PG is not an infection caused by bacteria, and it is not “gangrene” in the traditional sense ^[1][2]. Instead, it is a sign of a complex innate and adaptive immune dysregulation.

A Rare Immune Misfire

PG is exceptionally rare, affecting an estimated 3 to 10 people out of every million each year ^[3]. Because it is so uncommon, many patients spend weeks or months searching for answers while their wounds are misidentified as simple infections or surgical complications ^[4].

At its core, PG is a neutrophil-predominant autoinflammatory disorder. In most autoimmune diseases, the body mistakenly creates antibodies to attack its own healthy tissue. In PG, the problem lies with the “first responders” of the immune system—specifically cells called neutrophils ^[2]. These white blood cells are supposed to rush to a site of injury to kill bacteria and then quiet down so healing can begin. In people with PG, research suggests these cells are overactive, flooding the skin with inflammatory chemicals even when no infection is present ^[5]. This creates a sterile, aggressive inflammatory environment that destroys healthy skin instead of repairing it ^[1].

The Role of T-Cells and Cytokines

While neutrophils do the visible damage, other parts of your immune system act as the “engine” behind the inflammation. Research suggests that T-cells (another type of white blood cell) may be among the first to arrive at a new site, signaling the body to start an inflammatory response ^[6]. These cells release chemical messengers called cytokines—such as TNF-alpha, IL-1 beta, and IL-17—which act like an alarm system that won’t turn off ^[7][8]. This continuous “alarm” keeps the neutrophils in a state of high alert, leading to the characteristic rapidly spreading, “undermined” edges of a PG ulcer ^[9].

Understanding Pathergy: When Trauma Triggers Trouble

One of the most defining and frustrating features of PG is a phenomenon called pathergy ^[10]. This occurs when a minor injury to the skin—something as small as a needle stick, a scratch, or even a surgical incision—triggers the development of a new ulcer or causes an existing one to grow significantly larger ^[11].

Pathergy affects roughly 16% to 28% of people with PG ^[12][13]. It happens because the immune system in patients with PG is “primed” to overreact. When the skin is broken, the normal signal to start healing is misinterpreted as a signal to launch a massive inflammatory attack ^[1]. This is why doctors may be very cautious about performing biopsies or surgery on you while the disease is active; they weigh the possibility of pathergy against the need for a clinically important tissue sample ^[14].

The Emotional Impact of the “Invisible” Cause

Living with PG can be an isolating experience. The ulcers are often deeply painful, and because the cause is internal (immune-driven) rather than external (an infection), it can be difficult for others to understand why the wound won’t heal with standard care. The intense pain and the speed at which the skin can change are valid reasons to feel overwhelmed.

Recognizing that this is a systemic immune issue—not a failure of hygiene or a simple wound—is the first step toward finding the right management plan. While the biological “misfire” is complex, identifying the roles of neutrophils and pathergy helps your medical team move away from ineffective antibiotics and toward treatments that can calm the immune system’s overreaction.