Chemotherapy targets rapidly dividing cancer cells but often affects other fast-growing cells, including those in the skin, hair, and nails. A common side effect is a change in skin color, medically termed hyperpigmentation, which is a darkening of the skin. This discoloration is a recognized consequence of many chemotherapy regimens and is not typically a sign of the cancer worsening. Understanding how this darkening manifests and the biological processes behind it can help patients manage this visible change.
How Chemotherapy Affects Skin Color
Skin darkening caused by chemotherapy can present in diverse ways, ranging from a slight overall tan to distinct patterns. Some patients experience diffuse or generalized darkening, making the skin appear tanned, especially in sun-exposed areas. This generalized discoloration often appears a few weeks after chemotherapy begins.
Localized hyperpigmentation is common and tends to occur in areas subjected to friction, pressure, or inflammation. Skin folds, creases, scars, and areas beneath dressings often show a more pronounced darkening. Certain chemotherapy drugs administered intravenously can cause serpentine supravenous hyperpigmentation, appearing as a dark, linear streak following the path of the infused vein.
The nails are frequently affected, a condition known as melanonychia, where the nail plate or bed darkens. This may appear as a diffuse darkening across the entire nail or as horizontal or vertical dark bands. Drugs like bleomycin can cause flagellate hyperpigmentation, characterized by dark, whip-like streaks on the trunk and limbs, often appearing in irritated areas.
The Biological Reason for Hyperpigmentation
The underlying reasons for chemotherapy-induced hyperpigmentation generally fall into three main categories. The most common mechanism involves the direct stimulation of melanocytes, the skin cells responsible for producing melanin. Chemotherapy agents trigger these cells to increase their melanin output, causing the skin to darken. This reaction is similar to how the skin darkens in response to sun exposure or hormonal changes.
Another mechanism involves the direct deposition of the chemotherapy drug or its metabolic byproducts within the dermal layers. Certain drugs, such as busulfan, can accumulate in the skin, resulting in a diffuse, slate-gray or blue-gray discoloration. This discoloration may resemble the pigmentation seen in Addison’s disease. This accumulation of foreign substances, rather than just melanin, contributes to the color change.
Localized darkening is often a result of post-inflammatory hyperpigmentation. Chemotherapy can cause minor cellular damage or inflammation, especially in areas of trauma, friction, or sun exposure. The skin’s healing response includes an increase in melanin production and its release into the surrounding tissue, leaving a dark mark once the inflammation subsides.
Managing Skin Darkening and Reversibility
Managing skin darkening during chemotherapy centers on protecting the skin and minimizing factors that worsen hyperpigmentation. Sun protection is important because chemotherapy agents increase the skin’s sensitivity to ultraviolet (UV) radiation, which can intensify the discoloration. Patients should use a broad-spectrum sunscreen (SPF 30 or higher) every day, even indoors. They should also wear protective clothing and wide-brimmed hats when outside.
Gentle skin care is advised to reduce irritation that could lead to post-inflammatory darkening. Using mild, fragrance-free cleansers and rich moisturizers helps maintain the skin’s barrier function and minimize dryness or itchiness. Avoiding friction from tight clothing or rubbing prevents localized hyperpigmentation in areas like the groin, underarms, or joints.
For most patients, chemotherapy-induced hyperpigmentation is a temporary side effect. The discoloration typically begins to fade gradually after treatment completion as the skin naturally regenerates. This fading process can take several months, often between ten weeks and a year, depending on the specific drug and the patient’s skin type. While most changes resolve completely, a small percentage, particularly that caused by direct drug deposition, may persist long-term or become permanent. Patients experiencing persistent or bothersome skin changes should consult their oncologist or a dermatologist to rule out other causes and discuss management strategies.