Biodots are small self-adhesive temperature-sensitive discs that can be stuck to the skin. They indicate changes in skin temperature by changing colour.
How do biodots monitor stress?
Remember what you learnt about the stress response and skin temperature. Biodots monitor skin temperature changes caused by differences in the amount of blood flowing through the skin. More blood flow – skin is warmer; less blood flow – skin is cooler.
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When a person is tense and stressed blood vessels constrict, reducing skin blood flow, thus lowering the temperature of the skin. The biodot will appear yellow, amber or black. When a person is calm and relaxed blood vessels dilate, increasing skin blood flow, and this raises the temperature of the skin. The biodot will appear green, turquoise, blue or violet.
How to use biodots.
Stick the biodot where it will be easily seen but not easily dislodged. Recommended sites are on the inner surface of the wrist, and the base of the thumb and forefinger (see Figure 21). If care is taken the biodot can remain attached to the wrist or hand for several hours.
Other factors affecting biodot colour.
It is important to remember that certain conditions and activities apart from your level of stress response activation will affect biodot colour changes. These include:
Ambient temperature If the external temperature is cool or  cold the skin blood vessels constrict (biodot colour in black/amber/yellow range). If it is warm or hot the skin blood vessels dilate (biodot colour in green/blue/violet range). When you have acclimatized to the prevailing temperature any change in colour will indicate a change in the level of stress.
Exercise Colours indicating high stress levels (black/amber/yellow) will be observed when you are taking moderate exercise and going about your daily activities, even though you may not be emotionally stressed or tense.
This is because the skin blood vessels constrict during exercise, allowing more blood to flow to the muscles. In severe exercise, when the body is hot, the skin blood vessels will dilate allowing heat to be lost (biodot colour in green blue/violet range).
Alcohol consumption and smoking Alcohol dilates blood vessels and the biodot will show green, blue or violet.
Smoking causes constriction of the blood vessels and the biodot may appear black, amber or yellow.