I never have had a full beard. I am regularly more scruffy than I should allow myself to be and that does not cause enough of a problem to render the mask ineffective. If I'm particularly scruffy I would say it exposes me to perhaps 5% of the NH3 smell that I would normally be exposed to.

If you've been around NH3 for awhile you can take a little whiff of air and decide whether or not you want to keep breathing in and breath through the smell or whether you want to get to clear air before you take a full breath. If I'm really scruffy but I'm wearing a mask I have never encountered a situation where I took a test breath and decided I needed to move to clear air before breathing more. This includes when I was working on getting the safety coupler put back together after the hitch pin feel out and the weight of the tank pulled on the hose causing the safety coupler to separate. We purged the rig before starting to put it back together but the hose at the back was still spurting as we worked on it, occasionally shooting liquid out that got trapped in low spots in the hose. I was wearing the mask and gloves and a coat (all skin was covered except for a small area of my throat) while some liquid NH3 shot out and I smelled NH3 at that time but it was barely noticeable. I attribute the fact that I smelled it to the following things:

1. I was scruffy

2. I could have tightened the mask a little tighter

3. I was on top of the rig, bending over while working on the coupler so the weight of the mask was hanging down away from my face, decreasing the pressure of the seal against my face slightly

In every other situation so far, scruffy or not, I have not even smelled the NH3. With all that being said, I think it works significantly better when clean shaven vs scruffy so I wouldn't expect great results with a full beard.