A very good IT professional I worked with told me that they are difficult to wash because the water gets inside. so the best way is to clean them with malt whisky on cottonwool because the whisky evaporates and deosn't leave a lasting dampness.
however he did add that, considering the cost of malt whisky by far the best method was to drink the whisky then throw the mouse in the bin and ger a new one, it's cheaper.