Antimicrobial-treated balaclavas use silver ion or similar treatments on synthetic fabrics to fight odor-causing bacteria, and they do work well for 1–2 days between washes. If you're doing a weekend ski trip and prefer the quick-drying feel of synthetic fabric, this treatment keeps things fresher than untreated options.
The catch is that the treatment isn't permanent. With repeated washing, the antimicrobial effectiveness gradually degrades, so a balaclava that handled two days easily when new might start getting funky sooner after a season or two of use. It's not a dealbreaker, but it's worth knowing upfront.
If you regularly go on trips longer than a couple of days, merino wool is the stronger choice—it's naturally odor-resistant and won't lose that property over time. But for general resort skiing where you wash between uses, antimicrobial synthetics hit a nice balance of performance, durability, and price.