Stages of Heat Rash

Heat rash follows a fairly predictable course. Knowing the stages helps you tell a normal rash from one that needs care.

Stage 1: Sweat is trapped

In hot, humid conditions, sweat ducts block. You may feel only a slight prickling or tingling before anything shows.

Stage 2: Rash appears (hours)

Tiny clear blisters or red bumps appear on covered skin or in folds. Itching and prickling may increase with sweating.

Stage 3: Peak (1 to 3 days)

The rash is most noticeable and itchy. If the skin stays hot and sweaty, it may worsen.

Stage 4: Settling with cooling

When the skin is kept cool and dry, the ducts reopen. Redness fades, blisters dry up and itching eases, usually within 2 to 5 days.

Stage 5: Peeling and recovery

Mild flaking may occur as the skin heals. Normal skin returns, usually without scarring.

When the course goes wrong

• Infection: scratching can introduce bacteria. Signs include pus, crusting, spreading redness, pain, warmth and fever.
• Repeated episodes: may lead to deeper miliaria with reduced sweating.
• Heat illness: very high temperature, confusion or fainting needs emergency care. Call 112 or 102.

What to do at each stage

Early cooling prevents progression. If there is no improvement in 3 to 5 days, or signs of infection, see a doctor.

Key point

The earlier you cool and dry the skin, the faster it settles.

Before your appointment

Note when the rash began, where it is and what makes it better or worse, such as heat, clothes, creams or sweating. List any products, medicines, oils or herbal pastes you have used, and whether anyone at home has a similar rash. For a baby, note fever, feeding, and what the baby wears and sleeps in. Take photos of the rash over a few days.