I don't know about it getting thinner per se', but usually it'll become drier. I wash mine usually every other day, unless I do it curly, and it becomes a rats nest from sleeping - then I'll wash it again the next day. You want to give the scalp's natural oils a chance to coat the hair, and too much cleansing can leave your ends stripped of moisture, and your roots even more oily. (Since over-washing makes your scalp produce MORE oil, thinking it has none - from the washing) :icon_cool