These are the steps, which happen when a cavity is forming and causes long term damage:
- White spots: When your teeth are at the start of decaying, you'll notice white spots on your teeth. So most of your teeth may be yellow, then you have spots of white.
 - Enamal Decay: At this point, your teeth will start decaying underneath the surface of the tooth.
 - Dentin Decay: Next, acid and anything harmful to your teeth will dissolve your teeth. If decay moves to your dentin, your tooth will start to experience sharp pain.
 - Involvement of The Pulp: At this point, the pulp within your teeth may become infected by bacteria. 
 - Abscess Formation: Then, if the infection reaches the top of the tooth. It could cause swelling, and make the chance of you getting other diseases.
 - Tooth loss: Tooth loss is by far the worst part, by this time your teeth will start falling of due to being severely infected. 
 
If you ever see any of these signs, I advise you too see a dentist. Not seeing a dentist, could have bad affects on your health.
I hope this helps! :)
-LizzyIsTheQueen