Controlled openings
Fine needles create controlled channels through the epidermis. The skin becomes red and then repairs. Over several sessions, texture may become more even or a superficial scar less noticeable, but the response varies and cannot be guaranteed.
What it is not
A medical microneedling procedure is not equivalent to a home roller. Controlled depth, sterility and the decision not to treat diseased skin are essential. Nor is it a peel: the skin is punctured rather than a layer being removed.
The time repair takes
Judging the result the next day, under the redness, is useless. The spacing of sessions should let the skin finish what it has started. Adding a strong acid the same day, or a weekend of sun, cancels the care taken with the setting.