0.5mm Allure Derma roller These are the smallest needle lengths that will actually induce collagen. They will also of course increase trans-dermal absorption so they are very effective for both treatments. Generally, you need to use the smallest needle length you can to achieve the results you require, the simple reason is that it is painful, unnecessary and uncomfortable to use longer needles and you will not continue with the treatment. Therefore, for all general anti-aging purposes across the face, a 0.5mm roller is all you need at home to achieve results if your primary treatment is anti-aging and just improvement of the facial texture.