Answer to ... What do gluten and MSG have in common?

They're found in some of the same ingredients like

hydrolyzed wheat protein
stearyldimoniumhydroxypropyl (hydrolyzed wheat protein)
hydroxypropyltrimonium (hydrolyzed wheat protein)
hydrolyzed malt extract
hydrolyzed vegetable protein
maltodextrin (can be from barley)

These ingredients can be found in food as well as cosmetics and personal care products. So they can be enter your body either when you eat food containing these chemicals or when you apply products to your skin that contain them.