I'm having a devil of a time trying to get rid of fireflies in a render (files and an .exr frame attached). I've isolated it to the direct reflection pass (the hotspots along the nose in the pic), and Nuke tells me they are way hot superbrights. Doing the usual Google fixes (working with diffuse limit, boosting reflection quality and overall render quality, &c.) haven't changed anything. In the scene I have three lights and surprisingly it's not the environment light that's causing the problem (I isolated the lights and also boosted the sampling quality on the environment light), but the key light (a spot light, but I tried distant and area lights with the same result).

This is my first time dabbling with Substance Painter, which I used for a quick not-too-boring look, and it looks like the problem might be with the roughness or metallic maps. They're .tgas, and open fine in Photoshop. If I turn off all maps and boost the roughness the hotspots are less hot and spotty, but I don't think that's actually causing the problem.

I'm sure this is something easy and stupid. Thanks for any assistance!

(Credit where due: the original bust is from a photoscan by Ryan Baumann on Sketchfab.)

If they're in the direct reflect, then they are not fireflies. The hot spots are the specular reflection of a very small light source.

Normally, you don't need to worry about it unless it's causing aliasing.

In that case increase pixel samples and try using a larger pixel filter. It's normal to apply a bit of a blur/bloom in comp to blow out the hot speculars.

If you don't wan them at all, then change your lighting by diffusing the small light sources and/or increasing the roughness to be at least 0.1