Reported tDCS side effects are very few, and only experienced by a small number of the population. Some side effects associated with tDCS include a tingling or itching sensation during stimulation, a slightly metallic taste, and occasional redness at the site of the electrodes. Any redness usually fades away shortly after stimulation. An even smaller percentage of the population reports a slight headache as a tDCS side effect, however this also usually subsides shortly after the session is concluded. The most least reported tDCS side effect, which is usually attributed to improper use of electrodes or poorly assembled/prepared electrodes, is skin irritation. Sometimes this irritation can take the form of a small skin bump or lesion. However, it is important to note that even this side-effect is quite minor, and will fade away over a short period of time.
We found a great infographic on tDCS side effects located at tdcsbrainstorm.com, which shows that often most side effects can be attributed to the placebo effect. The results shown below depict that based on clinical trials, those individuals receiving "sham" stimulation (fake, no current) often reported the same symptoms at similar severity levels compared with those individuals receiving active stimulation (real tDCS).