Vinyl temperature strip card for baby: forehead sticker thermometer

what is forehead sticker thermometer?


A liquid crystal thermometer, temperature strip or plastic strip thermometer is a type of thermometer that contains heat-sensitive (thermochromic) liquid crystals in a plastic strip that change colour to indicate different temperatures.[1] Liquid crystals possess the mechanical properties of a liquid, but have the optical properties of a single crystal. Temperature changes can affect the colour of a liquid crystal, which makes them useful for temperature measurement. The resolution of liquid crystal sensors is in the 0.1°C range. Disposable liquid crystal thermometers have been developed for home and medical use. For example if the thermometer is black and it is put onto someone's forehead it will change colour depending on the temperature of the person.

There are two stages in the liquid crystals:

  1. the hot nematic stage is the closest to the liquid phase where the molecules are freely moving around and only partly ordered.
  2. the cold smectic stage is closest to a solid phase where the molecules align themselves into tightly wound chiral matrixes.

Liquid crystal thermometers portray temperatures as colors and can be used to follow temperature changes caused by heat flow. They can be used to observe that heat flows by conduction, convection, and radiation.

In medical applications, liquid crystal thermometers may be used to read body temperature by placing them against the forehead. These are safer than a mercury-in-glass thermometer[citation needed], and may be advantageous in some patients, but do not always give an exact result, except for the analytic liquid crystal thermometer which shows the exact temperature between 35.5 to 40.5 Celsius.

 Fever Temperatures: Accuracy and Comparison

You can take a temperature using the mouth (oral), anus (rectal), armpit (axillary), or ear (tympanic). But the temperature readings vary depending on which one you use, and you need an accurate body temperature to determine if a fever is present.

Medical research hasn't determined an exact correlation between oral, rectal, ear, armpit, and forehead temperature measurements. Generally, the correlation of temperature results are as follows:

  • The average normal oral temperature is 98.6°F (37°C).
  • A rectal temperature is 0.5°F (0.3°C) to 1°F (0.6°C) higher than an oral temperature.
  • An ear (tympanic) temperature is 0.5°F (0.3°C) to 1°F (0.6°C) higher than an oral temperature.
  • An armpit (axillary) temperature is usually 0.5°F (0.3°C) to 1°F (0.6°C) lower than an oral temperature.
  • A forehead (temporal) scanner is usually 0.5°F (0.3°C) to 1°F (0.6°C) lower than an oral temperature.

It is important to remember:

  • Rectal temperatures are generally thought to be the most accurate for checking a young child's temperature.
  • The manufacturer of the temperature device you use, such as an ear or forehead thermometer, provides information on how to use it. Be sure to read and follow the instructions to obtain an accurate temperature. The information may also include how the results of the device correlate with the results from other methods of taking a temperature.
  • Plastic strip thermometers have some uses, but they aren't recommended for general home use. Unlike oral, rectal, and ear thermometers, plastic strip thermometers measure skin temperature, not body temperature.

When you talk with your doctor about your temperature, be sure to say what method was used to take the temperature.

Temperature comparison table

The temperature comparison table below will give you the range of temperature correlation with the different methods used to take a temperature. For information about taking accurate temperatures in infants and children, see the topic Body Temperature .

To use the table:

  • Find the method that you used to take a temperature.
  • Find the correct temperature range.
  • Look for the temperature range of the other methods that correlates to the method you used. For example:
    • If your 2-year-old child's oral temperature is 101°F (38.3°C), his or her rectal or ear temperature may be about 102°F (38.9°C). Remember, a child has a fever when his or her temperature is 100.4°F (38°C) or higher, measured rectally.
    • If your axillary temperature is 100°F (37.8°C), your oral temperature is about 101°F (38.3°C).
Comparison of temperatures in Fahrenheit by method
Axillary/Forehead (°F)Oral (°F)Rectal/Ear (°F)



Comparison of temperatures in Centigrade by method

Axillary/Forehead (°C)Oral (°C)Rectal/Ear (°C)



Thermochromic Liquid Crystals (LCs) can be highly temperature sensitive, change to many colors, and are more expensive than leuco dyes. LCs start black below their temperature range, go through the colors of a rainbow, and back to black again above the temperature range. LCs are reversible in that they can be used over and over again. The picture shows an example of a liquid crystal sheet in response to warming.

Popular liquid crystal applications include medical devices, forehead, aquarium and room thermometers, promotional pieces and advertising applications. Additionally, functional devices such as propane tank gas level indicator are achieving much notoriety. Liquid crystal thermometer strips are being used for thermal mapping and other industrial applications where custom inexpensive temperature monitoring is warranted. We offer a wide range of liquid crystal thermometers as stock products, but also offer literally thousands of custom products for your label.

LCs are very similar to the liquid crystal displays used in watches and laptop computers, but our thermochromic LCs change color with temperature instead of voltage. LCs can be formulated to change temperature from -22 to +248ºF (-30 to 120ºC), and can be sensitive enough to detect changes as small as 0.2ºF. If kept out of UV light and away from high temperatures and strong solvents, LC products will last for years.

The most prevalent use of liquid crystal is as a self adhesive reversible temperature indicator label that continually monitors temperature offering a visual readout that ranges from traditional numeric displays to custom graphics that can serve as an alert or warning.


These self-adhesive labels consist of a series of temperature-sensitive elements containing Microencapsulated Thermochromic Liquid Crystal (TLC) coated on a black backing. Each element changes color distinctly as its rated temperature is reached, passing through the colors of the spectrum in sequence from tan to green to blue before turning black at a higher temperature). The TLC strips are calibrated so that the indicator that shows green indicates the actual temperature. The color changes are reversible and the reflected colors will be observed in the reverse order upon cooling.


The temperature-sensitive elements contain TLC molecules that are very sensitive to temperature and change position / twist in relation to changes in temperature. This change in molecular structure affects the wavelengths of light that are absorbed and reflected by the liquid crystals, resulting in an apparent change in the color of each temperature event.

When the rated temperature of an indicator is reached the TLC molecules twist slightly causing the TLC substance to absorb the red and blue portions of the visible light and reflect the green part. This causes the temperature event to appear green. When the temperature decreases, the molecules begin to twist in the opposite direction, and the TLC reflect a different portion of the spectrum.


In addition to the standard Digi-Temp labels available, which cover the temperature range of -30 - 120°C, a full custom manufacturing service is available and products can be manufactured to meet customers' precise requirements of, size, shape, color, temperature range, number of temperature elements, graphic printing (logo's etc). Please ask for details!