Does heat rash spread?

Why can more spots appear?

Heat rash develops when sweat gets trapped beneath your skin because sweat glands become blocked. More affected skin does not mean an infection is travelling from one spot to another. Heat and excessive sweating are the problem, particularly in hot, humid weather. Sweat normally cools you when it reaches the surface and evaporates. Most sweat glands are distributed across your body, and heat can trigger sweating in many areas rather than just one patch.1345

Typical heat rash has small, raised spots, an itchy or prickly feeling and mild swelling. Some spots contain fluid. The rash can appear anywhere, and symptoms are often similar in adults and children. Spots look red on white skin; on brown or black skin, they can look grey or white and be harder to see.1

What should you do if heat rash is spreading?

Start by reducing heat and sweating rather than adding more skincare. Cooling is the main job here, not assembling a bathroom shelf with its own management structure.1

1. 1Move somewhere cool and pause activity that keeps you hot and sweaty.
2. 2Change into loose cotton clothing and use lightweight bedding.
3. 3Take a cool bath or shower, then keep the affected skin cool and dry.
4. 4Soothe itching with a damp cloth or an ice pack wrapped in a tea towel for up to 20 minutes.
5. 5Tap or pat itchy skin instead of scratching, and avoid perfumed shower gels or creams.

Avoid emollients, meaning moisturizers, on heat rash. A pharmacist can advise about calamine lotion, antihistamine tablets or hydrocortisone cream for symptoms. Get a doctor's advice before using hydrocortisone for a child under 10. For a child with heat rash, moving to a cool place helps stop sweating and allows the rash to settle.124

How long should it take to settle?

Heat rash usually improves on its own within a few days. See a doctor if it is not improving after that, or if your baby has a rash that worries you. For children, persistent bumps deserve a check because different rashes can look alike; appearance alone is not enough to identify the cause.12

When does a spreading rash need medical help?

• Contact a doctor for severe pain, constant itching, fever, or blisters around the eyes, mouth or genitals.
• Get medical advice for warm skin, pus, yellow or green fluid, or red streaks around the rash. These can indicate infection.
• Seek immediate medical attention for a sudden rash that spreads quickly, trouble breathing or facial swelling.
• For an unwell child, get emergency help for confusion, breathing difficulty, a stiff neck, or a rash resembling bruises that does not fade when pressed with a glass.

Dizziness, nausea, vomiting or headache after heat exposure can indicate heat exhaustion rather than just heat rash. Seek immediate medical care and move out of the heat. Confusion, behaviour changes or slurred speech can indicate heat stroke, which is a medical emergency. A heat rash does not have to cause a high body temperature.4

How can you reduce another flare?

Limit time in the heat, avoid prolonged exercise in hot conditions and drink fluids to prevent dehydration. Loose clothing helps keep skin cool, so a summer wardrobe need not double as insulation. Heat rash is more common in babies and young children, although any age can be affected. Older adults, young children and people taking certain medicines also have a higher risk of heat illness. If your sweating changes noticeably, ask a healthcare professional about the change.3457