Purpose: Bluetooth is a standard wire-replacement communications protocol primarily designed for low-power consumption, with a short range based on low-cost transceiver microchips in each device. Because the devices use a radio (broadcast) communications system, they do not have to be in visual line of sight of each other, however a quasi optical wireless path must be viable. Range is power-class-dependent, but effective ranges vary in practice; see the table on the right.
Officially Class 3 radios have a range of up to 1 metre (3 ft), Class 2, most commonly found in mobile devices, 10 metres (33 ft), and Class 1, primarily for industrial use cases,100 metres (300 ft).
Issues: Like all of the other things on this site, blue tooth uses frequencies that are biologically active - they cause cellular damage. The worst offenders in the blue tooth spectrium are those things that sit on the head - things like headphones, ear buds, headsets and glasses. What makes them bad is that they have an antenna that receives (collects) the blue tooth frequency at your head. These are best avoided.
Frequency Range: Wi-Fi and Bluetooth both occupy a section of the 2.4 GHz ISM band that is 83 MHz-wide. Bluetooth uses Frequency Hopping Spread Spectrum (FHSS) and is allowed to hop between 79 different 1 MHz-wide channels in this band.
Wi-Fi uses Direct Sequence Spread Spectrum (DSSS) instead of FHSS. Its carrier does not hop or change frequency and remains centered on one channel that is 22 MHz-wide. While there is room for 11 overlapping channels in this 83 MHz-wide band, there is only room for three non-overlapping channels. Thus there can be no more than three different Wi-Fi networks operating in close proximity to one another.
Better Option: Keep the Blue Tooth features of your electronic devices turned off. Do everything that you can wired. Do not put blue tooth devices on your head or in your ear. It is best not to use them in your vehicle, where the metal will cause the signals to bounce about and not dissipate.
Source:
http://www.hp.com/rnd/library/pdf/WiFi_Bluetooth_coexistance.pdf
https://en.wikipedia.org/wiki/Bluetooth