Never
put electrodes over the eyes, in the mouth, over broken skin,
over a rash or psoriasis, over the front of the throat, in
the chest region if you have heart problems or a pace-maker,
or over the genitals.
Also,
never place electrodes in such a way that the stimulation would
travel through the uterus in times of pregnancy or menstruation.
Mostly, these are all situations that one would avoid as a
matter of common sense.
Never
put electrodes over the eyes, in the mouth, over broken skin,
over a rash or psoriasis, over the front of the throat, in
the chest region if you have heart problems or a pace-maker,
or over the genitals. 
Also,
never place electrodes in such a way that the stimulation would
travel through the uterus in times of pregnancy or menstruation.
Mostly, these are all situations that one would avoid as a
matter of common sense.