Why calamine feels cool as it dries
Calamine lotion is a water-based suspension: tiny particles of zinc oxide and colored iron oxide are dispersed through liquid rather than dissolved in it. After you spread on a thin layer, water at the surface evaporates. Evaporation takes heat from the skin, producing a brief cooling sensation—much like damp skin feeling cooler in moving air.
Cooling can interrupt the itch signal
Itch is a sensation carried by nerves in the skin. Coolness activates temperature-sensitive nerve endings, and those signals can temporarily compete with or distract from the itch signals reaching the brain. That can make the urge to scratch feel less prominent while the lotion dries and for a short time afterward.
The effect is sensory, not a cure for the cause of the itch. Calamine can also leave a thin, dry residue on the skin, which may soothe irritated areas, but the cooling itself mainly offers temporary relief. As the water finishes evaporating and the skin warms again, the sensation fades.
