Why Mirrors Fog Up: Condensation Physics Explained

Mirror fogging is condensation. Warm, moist air (exhaled breath or humid room air) contacts the cooler mirror surface. Water vapor loses kinetic energy, transitions to liquid, forming microscopic droplets that scatter light—creating a foggy veil.

Factors increasing fog:

• Higher humidity (more vapor available).
• Larger temperature difference between air and mirror.
• Smooth, non‑porous surface (droplets don’t absorb).

Defogging tricks: Pre‑warm mirror (hair dryer), apply thin surfactant film (shaving cream, soap, commercial anti‑fog), or increase ventilation to reduce humidity.