The difference between prickly heat (miliaria) and rash is quite significant. Firstly, prickly heat is a dermatological condition that often occurs in hot weather, heat, or when sweat cannot be excreted through the sweat glands. The main manifestations of prickly heat are visible papules and pustular papules. On the other hand, a rash is a manifestation and a symptom, often occurring in skin infections or diseases like skin allergies and eczema. Thus, prickly heat and rash are completely different concepts.