What could be causing my bath salts containing baking soda to explode out of their containers? I run a small herbal wellness business and one of the products i sell are bath salts containing baking soda. The base ingredients are Epsom salts, Dead Sea salts, magnesium chloride, baking soda, coconut milk powder, and fractionated coconut oil. I’ve made and sold this recipe for over a year and because i buy my ingredients in bulk i haven’t bought new ingredients recently. All of a sudden, some kind of chemical reaction is happening (which i assume is coming from the baking soda), and after i seal the bags they blow up like a balloon and then eventually explode. I cannot for the life of me figure out what is causing the baking soda to react. I’ve noticed when I’m mixing up batches that there is a fizzing sound that has never been there before, and I’ve wondered if the salts have somehow absorbed water. But water doesn’t really cause baking soda to react like this. Thanks for the help!
I suspect the seasonal introduction of humidity is the root of the problem, which is readily taken up by the magnesium chloride. Then, the following possible reaction:
$\ce{ MgCl2 (aq)  + 2 NaHCO3 (s) -&gt; 2 NaCl (aq)  + Mg(HCO3)2 (aq)}$
Now, aqueous Magnesium bicarbonate exists only in solution (so decomposes on drying), is not stable on standing (per my experience), or warming (whereupon it also decomposes):
$\ce{ Mg(HCO3)2 (aq) -&gt;  MgO (s) + H2O (l) + 2 CO2 (g)}$
where the pressurized buildup of carbon dioxide gas is likely causing a problem.
Solution: Try adding a drying agent or removing the very hygroscopic Magnesium chloride from your formulation.