It’s essentially a 2mm-thick micro-bearing in the shape of a ring, so anything getting inside would be a serious issue. The good news is that after sealing, the only opening is a 0.1mm side gap between the inner and outer rings — and in normal daily wear, nothing gets through. (I’ve worn it for 3 months with no buildup.)

Extreme cases like mud or beach sand are possible. In those situations, a gentle spin under running water should clear it out.