@melann77 0.25mm is purely for enhanced product absorption and can be done as often as every alternate day (although I personally wouldn't do it that often). 0.5mm is generally considered the safest depth to be used all over the face without having to adjust depth for certain areas to promote collagen production, treat fine lines, texture issues etc. General consensus on frequency of this depth is once a month. Personally at a depth of 0.5mm + I use basic formulations of hyaluronic acid only, the least amount of additional ingredients and stabilisers the better. Not so worried with 0.25mm. Always a good idea to start at 0.25 to see how your skin reacts.