Can I wear compression base layers for multiple days like merino wool?

Generally no. Most compression base layers are synthetic-dominant and develop noticeable odor after 1–2 days of active wear, compared to 5+ days for pure merino wool. The tight fit keeps fabric in constant contact with sweat and skin bacteria, accelerating odor development. If multi-day wear is important, look for merino-synthetic blend compression layers or compression layers with silver-ion odor treatments, though these still won't match pure merino's odor resistance.