When a skin lesion discharges fluid, especially a thick, discolored substance, the immediate fear often turns to skin cancer. While pus is an alarming symptom, it is a sign of the body’s immune response to an infection, not a direct product of the cancer itself. Understanding the difference between discharge from an infected lesion and the characteristics of skin cancer lesions is important for accurate assessment. This distinction helps clarify why a minor infection can sometimes mimic the advanced signs of a serious underlying condition.
Understanding Pus and Its Formation
Pus is a viscous fluid, commonly appearing yellowish, greenish, or white, that forms at a site of inflammation. Its composition consists primarily of dead white blood cells, specifically neutrophils, which are a type of leukocyte. These immune cells travel to the site of irritation or microbial invasion in response to chemical signals released during an infection.
After neutrophils engulf and destroy invading bacteria or fungi, they die off and accumulate along with destroyed microbes and necrotic tissue debris. This collection of cellular waste and fluid creates the characteristic thick texture of pus, a process known as suppuration. The distinct color often results from myeloperoxidase, a green antibacterial protein produced by the white blood cells, or from specific bacterial pigments. Pus is evidence of an active, localized immune battle against a bacterial or fungal pathogen.
Core Symptoms of Skin Cancer
The primary signs of skin cancer involve changes in the appearance, texture, or behavior of a spot on the skin, not the production of pus. For melanoma, the most serious form, doctors use the ABCDE criteria to identify suspicious lesions: Asymmetry, Border irregularity, Color variation, Diameter greater than 6 millimeters, and Evolving size or shape. Melanomas often present as moles exhibiting these characteristics, but they do not generate a purulent discharge.
Non-melanoma skin cancers, such as Basal Cell Carcinoma (BCC) and Squamous Cell Carcinoma (SCC), present as persistent, non-healing sores or scaly patches. BCC commonly appears as a pearly or waxy bump with rolled edges, while SCC often looks like a firm, red nodule or a scaly patch that may bleed easily. Advanced BCC and SCC lesions may ulcerate, forming a raw, open wound that bleeds or weeps clear fluid, but the tumor itself does not produce pus.
Discharge from a cancerous lesion is usually serous fluid or blood, resulting from the tumor tissue breaking down and the fragility of its blood vessels. Advanced skin cancers, particularly SCC, can sometimes discharge foul-smelling yellow keratin that may resemble pus. A key differentiator for BCC and SCC is an open sore that follows a cycle of bleeding, scabbing, and failing to heal completely over several weeks.
When Lesions Produce Discharge
When a skin lesion, whether benign or malignant, produces true pus, it indicates a secondary bacterial infection. A break in the skin barrier—through scratching, picking, or natural ulceration—allows pyogenic bacteria to enter the tissue. The resulting immune response leads to pus formation, which may then drain from the open wound.
Many common, non-cancerous skin conditions are more likely to produce a pus-filled discharge. These include abscesses, cysts, severe acne (pustules), or infected hair follicles (folliculitis). For instance, a benign sebaceous cyst that ruptures or becomes infected can release thick, purulent material. In these cases, pus is a sign of localized infection, not a symptom of cancer.
Understanding the difference between ulceration and pus production is important. Cancerous lesions frequently ulcerate, creating a crater-like depression that may weep clear fluid or blood. Pus—the thick, opaque, colored fluid—only appears when this open wound is colonized by bacteria. If pus is present in a skin lesion, it means an infection is occurring in or around the existing wound, regardless of the underlying cause.
When to Seek Professional Evaluation
Any skin lesion that exhibits persistent discharge, whether purulent or simply bleeding and oozing, requires a professional medical evaluation. A sore that does not heal within a few weeks, or one that repeatedly scabs over and reopens, is a significant warning sign that should prompt an appointment with a dermatologist. Pus, while likely indicating a treatable infection, should not be ignored, as a secondary infection can complicate the diagnosis and treatment of any underlying condition.
A healthcare provider will examine the lesion to determine the cause of the discharge and the nature of the lesion itself. They may recommend a biopsy, which involves taking a small tissue sample for laboratory analysis, to confirm the presence or absence of cancerous cells. Addressing the infection, often with topical or oral antibiotics, is the first step, but confirming the underlying cause of the lesion is necessary for comprehensive care.