If it shrinks that much after a day, the derm probably won't lance it, but would do a cortisone injection if anything. They most likely wouldn't just lance it anyway if it's a bad one or very deep, but maybe send you to have it surgically removed (meaning 4-5 weeks off the bike at least).

I've tried using a cortisone cream, and that really helps get rid of the inflammation. I put on neosporin to help any open or oozing areas (sometimes mine comes to the surface and ruptures on its own). I also use neosporin with my chamois cream for a ride. It seems to help keep the thing from being reinfected.

All it takes to get one is to have some irritation enough that bacteria gets under the skin. Add in a little pinch from the saddle or shorts and it can get out of control. So an ingrown hair could get the ball rolling on a saddle sore or just getting a little raw from friction and moisture.

Seriously, find a good dermatologist if you're that worried about it. It may just clear up on its own or at least stay manageable until it decides to go away.