Works great to hide thinning hair patches. Just shake on the areas that are thinning. Works by concealing balding scalp areas - the micro fibers lay on top of your scalp darkening the area so your otherwise shiny noggin doesn't show thru the thinning hair. Also somewhat thickens the appearance of hair. Withstands wind pretty well & moisture to some degree. Washes out easily with shampoo and water. Will also rub off on your hands if you run your hands thru your hair. Is purely a cosmetic fix to hiding hair loss. For it to work well, it's necessary for there to be some hair, even if it is fine and short, present to which the fibers can adhere and fill in. Best for concealing small patches. Causes me no irritation and don't even know I'm using it.