Why doesn't chewing gum dissolve, no matter how long you chew?

Chewing gum never dissolves because you were only ever meant to dissolve part of it. A stick of gum is two things pressed together: a water-loving cargo of sugar and flavorings, and a water-hating core called gum base — a chewy blend of polymers (long molecule chains that simply shrug off water), plus resins and waxes. Saliva strips out the sweet cargo within minutes and carries it down your throat. The base, being built from the same family of materials as rubber bands and bottle caps, cannot mix with water at all. You could chew until the next century; the base would stay a base.

Exhibit A: what a stick is actually made of

The insoluble base typically makes up somewhere between a fifth and a third of the stick by weight. Everything else — the bulk sweetener, the mint or fruit oils, the softeners — is designed to leave. That's why gum 'loses its flavor': nothing broke, the deliverable was simply delivered. What's left in your mouth afterward is the vehicle, not the payload.

Why saliva never stood a chance

Saliva is more than 99% water, and dissolving is a molecular handshake: water can only pull apart substances whose molecules it can grab onto, like sugar. The base's long chains hold hands with each other instead and present water with nothing to grip. Warmth and chewing soften the base — that's mechanics, not chemistry. Your stomach acid fares no better, which is why swallowed gum arrives at the other end recognizably itself.

The seven-year rumor, closed

No, swallowed gum does not camp in your stomach for seven years. Gastroenterologists are unusually cheerful on this point: the gum can't be digested, but the gut doesn't keep what it can't process — it just passes it along, intact, in a day or two. The myth got the chemistry right and the plumbing completely wrong.