Excellent odor resistance means the base layer can go 5 or more days of active skiing without developing noticeable smell. This level is almost always achieved with high-quality merino wool, which has natural antimicrobial properties that fight odor-causing bacteria—no chemical treatments needed.
This becomes genuinely valuable on multi-day ski trips, backcountry hut trips, or any travel where you won't have laundry access. Instead of packing a fresh base layer for every single day, you can get away with one or two for a week-long trip. It also means no awkward smells when you're sharing close quarters at a lodge or hut.
If you mostly do day trips and wash your gear between uses, excellent odor resistance isn't essential—a "good" or "moderate" rating will serve you fine. But there's a long-term advantage too: merino's odor-fighting ability is permanent, whereas synthetic treatments like silver-ion coatings wear off with repeated washing over time.