...you wouldn't know it by Ed's avatar, but a good shave really helps with the fit.
A Goatee can be shaped to fit inside those masks.
Every time you put on the mask, test the fit, by putting your hands over the intakes and breathing in, the mask should suck tight to your face.
Not only the formaldehyde in the micarta, we use a lot of solvents such as epoxies, CA glue and acetone.
VOC cartridges - (Volatile Organic Compounds) should help to protect against this.
They should be allowed to dry out after wearing and then stored to protect against moisture, which degrades effectiveness of the activated charcoal in the filters.
Cover the chemical filters with P100 overfilters to stop the dust.
If you ever smell any chemical smell, it's time to adjust the fit, or change the cartridges.
As Ed mentioned, there are different sizes of fits.
Go to an industrial safety store and they will try on different sizes to get you the right fit and the right cartridges.
I have used both 3M and North masks- especially the soft silicone face pieces.
There are cheaper masks in the hardware store with a harder plastic that don't fit as well and I am much more likely to take it off if it feels bad.
North half mask
http://www.labsafety.com/NORTH-7700-Series-Half-Mask-Respirator_24527529/
(Acid Gas = Formaldehyde)
Combo filter - Organic vapour and Acid GAs
http://www.labsafety.com/North-Organic-Vapors-Acid-Gases-Respirator-Cartridges-Pkg-of-2_s_41585/Cartridges-and-Filters_24530051/
The Dust Pre filter that snaps over the chemical filter
http://www.labsafety.com/North-P100-Pancake-Respirator-Filters-Prefilters-Disk-Type-Pkg-of-2_s_44302/Cartridges-and-Filters_24530051/
needs this adaptor
Use with Filter Adaptor (No. 44303)
-can't find a link for that-