I have a feeling that it blocks DHT at the follicle levels and therefore slows or stops the growth.  Which would also be good for hair loss on the scalp.  I have heard of rubbing saw palmetto onto the scalp can actually thicken hair there because this is how it works.  Amazing that something can do two different things in two seperate places.  Both thicken and thin hair dependant upon where it is and how it reacts to raised dht levels.