How does salt lower the melting point of ice and snow?

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Cluster of translucent, white salt crystals with sharp cubic shapes viewed under a microscope at high magnification against a dark background. — salt Salt crystal magnified.

Salt, or sodium chloride, lowers the melting point of ice through a process known as freezing point depression.1

At 32 °F (0 °C), water and ice exist in a state of equilibrium where the rate of melting and freezing is constant. When salt is added, it dissolves into sodium and chloride ions, which interfere with the ability of water molecules to bond into a rigid ice structure. Because the salt lowers the freezing point, the water cannot refreeze at 32 °F, yet it continues to melt the existing ice, effectively reducing the amount of ice on the ground.1

While effective, it is important to acknowledge that the use of chloride-based salts poses significant ethical and environmental concerns. Chloride can harm aquatic life, dehydrate plants, and degrade soil quality, which disrupts local ecosystems. Prioritizing environmental stewardship is essential when managing road safety in winter conditions.1