Skin reactions from medical devices range from minor erythema to severe necrosis - predicting dermal response requires testing that simulates actual clinical exposure including both intact and compromised skin barriers. Primary skin irritation testing per ISO 10993-23 evaluates dermal compatibility through topical application of polar and non-polar extracts to intact and abraded rabbit skin, providing essential safety data for all skin-contacting medical devices. The protocol applies 0.5 mL of extract to gauze patches placed on prepared skin sites for 4 hours, with subsequent observation capturing both immediate and delayed responses through scoring erythema and edema. Device categories requiring skin irritation data encompass all surface devices with skin contact exceeding momentary duration - wound dressings where direct contact proves prolonged, ostomy devices contacting compromised skin, compression garments worn continuously, electrode gels applied repeatedly, transdermal patches designed for extended wear, and external prosthetics requiring daily use. The abraded skin sites simulate compromised barrier function common in clinical use where wounds, inflammation, or repeated application damages stratum corneum, providing worst-case evaluation essential for risk assessment. For materials with borderline irritation, the test reveals whether effect intensity warrants usage restrictions, enhanced patient monitoring, or material reformulation preventing adverse events. The extract approach enables testing regardless of device configuration, accommodating complex geometries that preclude direct application while maintaining clinical relevance. Regulatory submissions require demonstrated low irritation supporting device labeling and patient instructions, with results influencing duration-of-use recommendations and contraindications for sensitive populations.