Will applying hyaluronic acid after microneedling thicken skin under eyes? Would it have any effect on lips?

Thanks for your question. I am not aware of any studies demonstrating the effect of topical hyaluronic acid penetration after or during microneedling. In general hyaluronic acid is a large molecule and would not easily penetrate substantially even with the channels created with microneedling. The reason hyaluronic acid fillers work in this area is usually through the filling effect changing the angles and shadowing that you get from the tear trough area. We utilize hyaluronic acid for the gliding agent when microneedling but it is more for the smooth glide than for the penetration of it. An option to consider for the under eye would be platelet rich plasma injection (PRP) as this has been shown to help under the eye for filling and discoloration if you are against traditional fillers. If doing PRP in this area caution must still be taken, just as with hyaluronic acid fillers complications can arise in this area so ensure you are seeking out a qualified injector.  Good luck.