MODEL RELEASED. Measuring body temperature. Strip thermometer being used to measure the temperature of the forehead of an 18-month-old girl. The strip contains liquid crystals that change shape and reflect light with changes in temperature. Different areas of the strip contain crystals that are designed to respond at different temperatures. A temperature of 36 degrees Celsius is normal. The strip thermometer can show if the child has a fever (a raised body temperature). A slight fever is mostly harmless, and helps the body to fight infection. However, a severe fever in a young child requires medical attention.