Basaalikerros

Basaalikerros, also known as the stratum basale, is the deepest layer of the epidermis, the outermost skin layer. It forms a single layer of basal keratinocytes resting on the basement membrane at the dermal–epidermal junction. The layer is tightly connected to the underlying dermis through hemidesmosomes and the basement membrane, which helps anchor the epidermis in place.

The basal layer contains several cell types essential for skin function. Predominantly, it houses proliferative basal keratinocytes that divide to renew the epidermis. Melanocytes, which produce pigment, reside in this layer and transfer melanin to neighboring keratinocytes, contributing to skin color and protection against ultraviolet light. Merkel cells, which function in light touch sensation, are also located in or near the basal layer.

Functionally, the basaalikerros serves as the regenerative source for the epidermis. New keratinocytes generated in this layer migrate upward through the other epidermal strata (spinosum, granulosum, and corneum), differentiating as they move and eventually flaking off at the surface. This renewal cycle, in healthy adult skin, typically takes about a month, though it can vary with age, location, and health.

Clinical significance lies in the basal layer’s role as the origin of basal cell carcinoma, the most common form of skin cancer. Basal cell carcinomas arise from mutations in basal keratinocytes and are usually slow-growing with a low metastatic potential. The basal layer is also involved in normal wound healing, where keratinocytes proliferate and migrate to restore the epidermal barrier after injury.