I am not talking about shaving but for the record I use an electric razor as do most men. It has been well documented that wetting the skin makes a spanking much more intense. Using the same implement, and with the same force a swat will sting a whole lot more.
I believe even wetting undergarments will also yield similar results. This has certainly made the phrase “slap on a little after shave” have a completely different meaning for me.
Although I have read quite a few articles on the subject and can personally attest to the effect, no one has offered an explanation. I think I can explain it.
Using billiards for an example, you chalk the tip of the cue to get a clean strike on the ball. In other words the cue does not adhere to the ball allowing for more advanced techniques. Talcum powder on the hands also enables the cue to slide easily through the fingers.
How does this apply in paddling? When the paddle strikes a dry butt, the paddle bounces off the target. Some of the impact is reflected and only some absorbed. When the skin is damp or wet the paddle sticks, and most of the force of the blow is absorbed. I think the sticking also explains why it stings so much more.
Now if the intention is to reduce the intensity of the spanking, a little scented powder can be applied to the skin. This can be a pleasant addition and prolong the anticipation and the spanking. To be completely honest I will use any excuse to rub a bare bum.
CS
crankyspanker 
Wetting the back of the panties and then spanking them 'til they're dry is one particularly devilish trick of D's.
Your theory is good…but I think it's more physiological than that. Water opens pores, which increases the surface area for the paddle's vibrations, thereby making it a more painful spanking.
It really does hurt more! But there's just something about a wet bottom spanking that I can't get enough of…
Thanks for the input. Its nice to know that you actually read this stuff. There is a lot of truth in what you say. After all everything really happens in the mind.
Emanuele