Heat rash in the mouth: what to know

Heat rash, or miliaria, results from blocked sweat ducts and is usually found on warm, covered skin such as the neck, chest, or back. The moist lining inside the mouth does not present like ordinary heat rash. Red spots, ulcers, white patches, blisters, or swelling in the mouth can accompany viral illness, irritation, allergy, thrush, or other conditions. A rash on the lips or surrounding skin may also be different. See information on [Skin Bumps](/symptoms/skin-bumps/) and [Skin Rash](/symptoms/skin-rash/).

Do not put heat-rash creams, steroid creams, oils, or fragranced products inside the mouth. Offer suitable fluids if swallowing is comfortable and avoid foods or drinks that clearly sting. For a baby, continue breast or bottle feeds as tolerated and track wet nappies. Keep the outside of the face cool, but do not use ice directly on skin. [Emollient Therapy](/treatments/medical-dermatology/emollient-therapy/) is for selected skin problems and is not a treatment for mouth lesions.

Seek urgent help for trouble breathing, swelling of the lips or tongue, drooling with difficulty swallowing, choking, unusual sleepiness, or signs of dehydration. Arrange prompt medical review for fever, painful mouth lesions, poor feeding, repeated vomiting, or a rash that is spreading. A clinician can examine the mouth and surrounding skin and decide whether treatment such as [Topical Corticosteroids](/treatments/medical-dermatology/topical-corticosteroids/) has any role; never apply one inside the mouth without explicit instructions. [Skin Redness](/symptoms/skin-redness/) elsewhere may provide useful context.

Ask what the lesions look like, whether a medicine, food, or infection could explain them, and what fluids and foods are suitable. Mention fever, cough, hand or foot spots, recent antibiotics, allergies, and changes in feeding.