What causes squamous cell skin cancer?

Ultraviolet radiation from sunlight or tanning devices can injure the DNA of keratinocytes, the cells that form much of the outer skin. Over time, repeated injury can allow abnormal cells to survive and multiply. Actinic keratosis is a rough, sun-damaged skin change that can sometimes develop into squamous cell skin cancer, although not every actinic keratosis does.

Risk is influenced by cumulative exposure, lighter natural skin, a history of sunburn, older age, immune suppression, and previous radiation or skin injury. A cancer can arise on skin that does not seem heavily sun-damaged, so a new or changing spot deserves attention.

Arrange a skin examination for a sore, scaly patch, wart-like growth, or crusted area that does not heal or keeps returning. A clinician may inspect the area and remove a small sample for laboratory examination. Until assessed, protect exposed skin with clothing, shade, and broad-spectrum sunscreen, and avoid tanning devices. Do not pick, burn, or use strong home treatments on a suspicious lesion.

Seek prompt medical advice for a spot that bleeds easily, becomes tender, grows, develops a firm edge, or changes in color or texture. Seek urgent help for heavy bleeding that will not stop with steady pressure, rapidly increasing swelling, or signs of infection such as spreading redness and fever. These signs do not identify the cause by themselves, but they should not be ignored.

Ask whether the area could be actinic keratosis or another skin condition, whether a biopsy is needed, how much sun damage is present, and how to check the rest of your skin. If you take medicines that suppress immunity, ask whether they change your skin monitoring plan.