Which characteristic defines a stage I pressure ulcer?

A stage I pressure ulcer is characterized by the appearance of non-blanchable erythema. This means the skin appears reddened and does not turn white when pressed. It is the earliest stage of ulcer formation, indicating that there is damage to the skin, but it has not progressed to a point where the epidermis is broken or tissue damage extends beyond the superficial layers.

In this stage, the skin may feel warmer or cooler compared to surrounding areas, and might be painful or itchy. The presence of intact skin with localized redness is crucial for diagnosis at this stage, differentiating it from more advanced stages where there is visible skin loss or deeper tissue involvement.