Which mechanism transfers heat to tissue by direct contact?

• A. Conduction
• B. Convection
• C. Radiation
• D. Evaporation

Answer: (A)

Heat transfer to tissue by direct contact happens through conduction. When a warmer object touches the skin, energy moves from the object into the tissue through molecular interactions at the interface, driven by the temperature difference. This requires physical contact and is governed by how well the two surfaces meet (contact), how large the temperature gap is, and how well the materials conduct heat. Conduction is distinct from convection, which needs moving air or fluid to carry heat; radiation, which sends energy as infrared waves without contact; and evaporation, which cools by changing a liquid at the surface to vapor rather than transferring heat into the tissue. In practical terms, a hot pack or any solid surface in contact with skin primarily heats tissue by conduction.