It is necessary to wash synthetic hair wigs after 18 to 20 wears at maximum otherwise they stink bad. A greasy, messy wig is definitely a turn off and it does more bad than good. Washing synthetic wig is nothing tedious; it does not any involve complex process either. You only need to grab the correct supplies in order to keep everything smooth.
Do remember that synthetic heat resistant wigs do not lose factory built styling, bounce & wave after they have been washed unless you treat them using heating tools. Letting them air dry would make your wig revert to its previous state; however if you had styled your wigs using an iron or a curler; you might not get its previous state back. Therefore,you will have to restyle it yourself.
Follow this site to find out the tutorial on washing wigs & restyling them