Cave photographers have to deal with a similar problem, where thin steam that's normally invisible can be seen in photographs taken with flash.
Steam is composed of fairly spherical droplets of water. These act in a similar way to road studs of the "cat's-eye" type - they reflect light directly back to its source. The solution is to move the light off-axis, so the reflection is no longer aimed at your camera (eye).
So take your head-torch off, and hold or attach it away from your line of sight. Attaching it to your belt is ideal, if you want to illuminate the ground - you now have less distance between the light and the target (though if you get it too low, you'll find that every rock casts a huge shadow, hiding your route).
This is the same principle as front fog lights on motor vehicles, which are low-mounted for the same reasons.