A marshmallow is a sugar-based confection that, in its modern form, typically consists of sugar, water and gelatin which is whipped to a spongy consistency, molded into small cylindrical pieces, and coated with corn starch.
Some marshmallow recipes call for eggs.
This confection is the modern version of a medicinal confection made from Althaea officinalis, the marshmallow plant. (source)
So can guinea pigs eat marshmallows?
Unfortunately they are far too sweet for guinea pigs to eat and are not good for their stomach’s.
They will probably turn their noses up at them if presented with one though.
They are generally a food to avoid feeding them.