Are there limits on how much you can reduce your alar base?

There definitely are limits as to by how much the alar base can be reduced. 1 cm total (5 mm on each side) seems like a lot. Please note that alar base reductions are not the only means to narrow nostrils and/or alar bases. Furthermore, there are many different types of alar base reductions. Changing the nasal tip position itself can change the alar base width as well. I recommend you see an experienced rhinoplasty expert for a consultation for a detailed and comprehensive analysis that is not limited to your alar bases only. Best wishes!

There are limits to what can be done with rhinoplasty. One centimeter would be a lot to reduce from your alar base, and I personally have never removed that much tissue. All of that said, if your anatomy included an excessively wide alar base, then a 1 cm removal could be appropriate.  I would recommend consulting with a board certified facial plastic surgeon who regularly perform rhinoplasty to explore your options. Especially if considering maneuvers that extreme, you would want a surgeon extremely proficient in nasal surgery.