How can you tell the difference between a heat rash and an allergic reaction?

Pores: Heat rash is usually concetrated around the sweat gland pores. It can be red small scattered dots. Allergic reaction is more confluent amd perhaps scaly.

Rash v Allergies: Heat rash develops when your sweat ducts become blocked and perspiration is trapped under your skin. Symptoms range from superficial blisters to deep, red lumps. Some forms of heat rash can be intensely itchy or cause a prickly feeling. Heat rash usually goes away on its own. Allergic reactions go away with removal of the allergen and return when re-introduced.