Ihonpinnan

Ihonpinnan is the skin surface, the outer boundary of the body’s largest organ, the skin. In Finnish medical usage, the term denotes the interface between the body and the external environment. The surface consists of the epidermis, most notably the stratum corneum, and the protective lipid film that covers it. The stratum corneum is made of corneocytes embedded in a lipid matrix, forming a barrier that limits water loss and blocks many microorganisms.

The skin surface features microrelief such as grooves and pores, and openings for sweat glands and hair follicles, which project through the surface and contribute to thermoregulation and secretion. The composition of the surface lipids—ceramides, cholesterol, and free fatty acids—creates a hydrophobic barrier and helps maintain hydration and pH.

Functions: protection against pathogens, chemical irritation, and UV radiation, regulation of transepidermal water loss, and sensory input through cutaneous receptors. The surface environment influences drug and cosmetic absorption and the skin’s microbiome.

Variation: thickness and properties vary by body site, age, ethnicity, and health. The palms and soles have a thicker stratum corneum, while facial skin is thinner and more reactive. Aging can reduce barrier function and hydration.

Assessment and care: measurement of transepidermal water loss and surface pH are used in research and clinical practice; skincare aims to preserve or restore barrier function with humectants, emollients, and appropriate pH.