A skin tag, medically known as an acrochordon, is a common, benign, small growth of the skin that appears on a stalk, or peduncle. These growths are clusters of collagen fibers and blood vessels covered by the epidermis, typically appearing where skin folds or friction occurs, such as the neck or armpits. While they are generally harmless, a sudden change in color can be alarming. However, the phenomenon of a skin tag turning black is often a predictable step in the process of natural or intentional detachment.
The Mechanism Why Skin Tags Turn Black
The darkening of a skin tag to purple, brown, or black is a direct result of ischemic necrosis. This occurs when the blood supply to the tissue is interrupted or completely cut off, which is common for a pedunculated growth. Since the skin tag relies on a stalk for its blood supply, any obstruction to the tiny blood vessels causes the tissue to be deprived of oxygenated blood.
The lack of oxygenated blood leads to tissue death, or necrosis, which manifests as a change in color. The tag progresses from its normal flesh tone to a dusky purple and then ultimately to dark black as the cells die and dry out. This dark, desiccated tissue is known as an eschar and is the body’s way of naturally sealing off the dead growth. When this process is complete, the necrotic skin tag shrivels and detaches from the surrounding healthy skin, often falling off painlessly within a few days to a week.
Intentional Removal Techniques Causing Necrosis
The most common reason a skin tag turns black is because a controlled method has been used to intentionally induce necrosis. These techniques are designed to strategically cut off the blood flow to the growth, leading to its detachment. The resulting color change is a sign of success, confirming the removal process is working.
A frequent method is ligation, which involves tying a fine thread or dental floss tightly around the base of the skin tag’s stalk. This ligature physically constricts the blood vessels, achieving the necessary loss of circulation that forces the tag into ischemic necrosis. After successful ligation, the tag should progressively darken over 24 to 48 hours, confirming the blood supply has been effectively occluded.
Cryotherapy, or freezing the tag, is another widely used technique that achieves a similar result. Liquid nitrogen is applied to the growth, destroying the tissue and blood vessels by freezing the cells. This destruction typically causes the skin tag to form a dark blister or scab that eventually falls away as the underlying skin heals.
Electrocautery uses heat to burn off the growth, which also causes immediate darkening of the tissue. This process is more instantaneous than ligation or cryotherapy, as the burning immediately destroys the vascular core. While effective, this method is typically performed by a medical professional.
When Color Change Signals a Medical Concern
While a skin tag turning black is often a positive sign of necrosis, a spontaneous color change without any attempted removal or obvious trauma warrants closer inspection. This can sometimes happen if a tag with a long stalk twists on itself, causing an accidental torsion that cuts off its own blood supply. If this spontaneous torsion occurs, the resulting black color is still due to necrosis, and the tag will likely fall off on its own in the following days.
However, there are specific warning signs that differentiate a benign necrotic skin tag from a potentially more serious skin lesion that may have been misdiagnosed. If the growth shows rapid or irregular growth, multiple colors (such as blue, red, or white), or has an irregular border, it should be evaluated by a dermatologist.
A change in color accompanied by persistent bleeding after detachment, increasing pain, or signs of infection are also reasons to seek medical attention. Signs of infection include spreading redness, warmth, or purulent drainage extending into the surrounding skin. Consulting a medical professional is the safest course of action if there is any doubt about the nature of the growth or if atypical symptoms are present.