Glass test

The glass test is a simple way of telling if a rash blanches. This means that when pressure is put on the skin, the rash fades.

The glass test is useful, because it enables a parent to tell whether a rash is worryingly serious or not.

To perform the glass test

• Take an ordinary clear glass (or plastic) tumbler
• Place it on the skin next to the spots
• Roll it onto the spots, applying firm pressure. Note that the normal skin under the glass goes white as the blood is pushed out of the tiny surface blood vessels
• If the spots fade when the glass is rolled over them, the rash isn't serious
• If a spot doesn't fade, it is a non-blanching rash, and needs urgent medical attention