Prickly heat, also known as heat rash or miliaria, is a skin rash caused by trapped sweat under the skin. Sweat can become trapped when the narrow ducts through which sweat travels to the surface become clogged. It tends to be more common in warmer, more humid climates and usually appears on the torso and thighs, especially where skin touches skin. The symptoms of prickly heat include itching, irritation (prickling), small blisters, and large, red areas on the skin. The rash often looks red, but this may be less obvious on brown or black skin. The symptoms of heat rash usually last 2 to 3 days and can be treated at home by keeping the skin cool and dry, wearing loose cotton clothing, and applying something cold, such as a damp cloth or ice pack (wrapped in a tea towel) for up to 20 minutes. A pharmacist can also help with heat rash by recommending treatments such as calamine lotion, antihistamine tablets, or hydrocortisone cream. If the rash does not improve after a few days or becomes infected, it is recommended to see a doctor.